How difficult could it be for some people to accept that a planet, a moon etc. could be just as or more important than they are ? ?

Depends on how you define importance.

For example the Earth itself is vastly more "important" than any individual of any species, because there are billions and billions of lifeforms here on Earth that depend upon the Earth's integrity. Is that what you mean?

Very difficult

Some people just have their Heads up their Posteriors squire

There's a much greater degree of homogeneity between worlds. If you look at moons in the solar system, most of them look the same. Though their chemical composition might be slightly different. There isn't much to explore when it comes to lifeless worlds. The most interesting ones experience a large amount of tidal forces. Enceladus has gysers of water, as the result of tidal forces. Io is the most volcanically active world in the solar system because of tidal forces. Europa is also one of the more geologically distinct objects for the same reason. The fact Callisto has many more craters than Ganymede suggests the latter had relatively recent volcanic activity. All the worlds mentioned have volcanic activity. Tidal forces on Earth are also a prerequisite for life.

Titan is also an interesting world because it's atmosphere is thicker than Earth's. It's hard to say how common such an object is. Titan is pretty far from Saturn, so tidal forces wouldn't be much of a factor. There's a chance there's even life on Titan. Either the geology of Titan is rare, or there's life. Nevertheless, barren rocks with no activity whatsoever predominate. Comets can be a bit more interesting than asteroids, because they have water. In any case, if there was a life form that explored the universe, it would get bored constantly seeing lifeless rocks. Depending on how rare a world like Titan is, such a world might be one of the perks of exploration. A planet with non-photosynthetic life might be about as uninteresting to a galactic explorer. Whichever event is rarer would be more interesting.

A big freeze is probably a prerequisite for complex life. Photosynthetic life evolved to sink to the sea floor as a result of a big freeze. On Earth, the entire planet froze, not once, but twice. Microbes needed to be physically larger in order to sink to the bottom of the sea floor. Also, the length of the genetic code is a prerequisite for complex life. Fungi has a much longer genetic code than prokaryotes. Waterbears (tardigrades) have a longer genetic code than fungi. We don't actually know if tardigrade-type organisms predate the Cambrian explosion. In any case, the Cambrian explosion is when Earth really gets interesting. No one knows how common such a planet is, but it would probably be more rare than a world such as Titan.

Complex life is interesting for the same reason a game of chess is interesting. Every state is unique. Complexity gives impetus for exploration. If Earth was the only planet with complex life in the extended Virgo cluster, exploring the universe would be quite tedious. Say that was the case, and a distant explorer from the Centaurus-Hydra cluster discovered Earth, they would probably stop exploring lifeless rocks, or worlds with only microscopic life, and spend a significant amount of time studying Earth. They would try to communicate with us. The fact they're not doing so suggests that either complex life is very common, or inter-galactic exploration is very rare.

The peak of star formation was around 10 billion years ago. Therefore, ~5 billion years ago would have been the optimal time for intelligent life to develop. Explorers from the Centaurus-Hydra cluster wouldn't need to be significantly more technologically advanced than current human tech, to reach Earth in 5 billion years. They would only need to travel at 3% the speed of light to reach us. The fact we can't detect them, speaks volumes. The Perseus-Pisces cluster is about twice the mass of the Centaurus-Hyrda cluster. Intelligent life from there would only need to travel 5% the speed of light to reach us in 5 billion years. Also, we were much closer to the Perseus-Pisces supercluster 5 billion years ago.

The fact there aren't aliens everywhere is pretty sad. There are two reasons to be optimistic though. If the anthropic principle is the only reason for life on Earth, then humans given enough time, can explore the Shapley supercluster, and more nearby objects already mentioned. In such a scenario, we'd be unlikely to find any complex life. It's statistically probable that if intelligent life didn't emerge 5 billion years ago, then it's so rare, that it only happened once within billions of light years. In such a scenario, exploring galaxies wouldn't be very exciting. However, humans or non-human life created by humans, can create life on other worlds. That's something to look forward to. Given the rapid pace of medical breakthroughs, there may be people alive today who can attain immortality.

Alternatively, life is common. So common that Earth wouldn't be very interesting to a life form that has explored thousands of galaxies. In such a scenario, it's statistically probable that most organisms capable of exploring multiple galaxies, already began their journey billions of years ago. The number of species that would find humans worthy of study, is proportional to the speed of travel. Faster travel, would mean there are fewer species that find humans unique. Nevertheless, it's virtually impossible that intelligent life is more common than worlds like Titan, unless worlds are colonized by intelligent life.

The James Webb telescope, and ground based telescopes that should be operational within the next four years, will resolve the Fermi paradox once and for all. They will discover the atmospheric composition of planets. If every rocky planet in the habitable zone has an oxygen-rich atmosphere, that would suggest suggest a very high statistical probability of intelligent life throughout the galaxy. If humans build devices that can detect short-pulse lasers from other star systems, we would even more concrete evidence of intelligent life. I believe this decade will be the most significant decade in astronomy. The decade we discover intelligent life.

There's a very strong bias towards intelligence on Earth. Beluga whales have brains three times the size of humans. That would be a waste of energy, unless it served some purpose. Dolphins have brains that are twice the size of a human brain. It's very expensive to have a such large brain. It's impossible for such a large brain to evolve, unless it has an advantage. Elephants have very good memories. Perhaps better memories than humans. When an elephant is born, it's brain is half the size it reaches as an adult. Meaning, the environment will significantly shape the microstructure of an elephants brain. There were at least 20 different branches of hominids. Apes developed large brains before humans existed. Even earlier, monkeys developed large brains. The bear wolf caused the terror bird and entelodon to go extinct because it was more intelligent.

The presence of large apes probably causes cats to be smaller. In the Amazon, jaguars are larger than bonobos. In Africa, gorillas are larger than leopards. In Borneo, orangutans are much larger than cats. The Bornean big cat only weighs 55 pounds. Orangutans are dwarf versions of the bipedal ape, gigantopithecus. Animals always evolve to be smaller when trapped on an island. They would have arrived during an ice age. There are two species of orangutans. One species most likely was trapped in Borneo 2 million years ago when the entire polar ice caps melted. In any case, not believing that intelligence is an evolutionary arms race, is akin to denying the theory of evolution. Furthermore, the fossil record suggesting that intelligence is an evolutionary arms race, is not confined to humans.

Birds have good visual memory. They can remember human faces. The gray parrot has a larger vocabulary than Donald Trump. Paraves, the ancestor to birds, evolved 200 million years ago. It was probably the first warm blooded animal in existence. It also probably had a longer genetic code than other dinosaurs. Some indication of this is that paraves shrunk 160 faster times faster than other dinosaurs were growing. Smaller is better. Rapid shrinking implies increased intelligence. The shrinking of paraves also coincides with the appearance of ants and other eusocial insects. The increased intelligence of paraves, either directly, or indirectly, caused an evolutionary arms race which extended all the way to eusocial insects. What makes eusocial insects such as ants and termites remarkable, is that they can build structures, which for their size, is comparable to the largest structures ever built by humans. Ants can even kill elephants, if they're not free to flee. That's several orders of magnitude more impressive than humans hunting whales. Peak sperm-whale oil wasn't reached till 1846.

Therefore, intelligence is an arms race. It's synonymous with the theory of evolution. The Scopes trial was in 1920, requiring the theory of evolution to be taught in schools. There's more evidence today that intelligence is an evolutionary arms race, than there was evidence for the theory of evolution a century ago. Beyond tardigrades, the number of chromosomes indicates intelligence. Amphibians have more chromosomes than insects. Reptiles have more chromosomes than amphibians. Birds have more chromosomes than reptiles. More generally, the length of the genetic code indicates increasing complexity. Of course, insects have a longer genetic code than tardigrades. It's not known how many chromosomes paraves had 200 million years ago. Paraves either increased their number of chromosomes, or it already had more chromosomes than reptiles and other dinosaurs as early as 200 million years ago.

More to the point, an uninhabitable world is roughly equal in value to a single individual. Furthermore, an entire species, maybe even a particular exceptional individual is of greater worth than an uninhabitable world. Titan may be habitable when the Sun becomes a red giant. A planet that's inhabitable in the future would be more valuable than any one human.

A planet or moon is not a living being.  Living things are more important than nonliving things.