I've seen enough movies and read enough books to be able to shunt that aside, and in fact in some cases say "yes the idea isn't original but they did it better this time". And I'd be more than willing to say this was the case with Avatar, if it was the case.
The problem with Avatar - a film I am surprisingly and unexpectedly finding myself disliking more and more 24 hours after I first saw it the more I think about it - is that the similarities are so overt and obvious that it distracted from the enjoyment of the piece.
Well, now that you have expressed your authoritative opinion, I guess we can put this thread to rest.

As for you disliking it more and more... Not that unexpected. It's a common theme in this thread amongst people who did not enjoy the film. After seeing/reading how popular Avatar is, it just vexes them to no end. But it's OK, you know. People like different things.
And it's not just the fact that Avatar borrowed the Gaia theory idea from Final Fantasy and also featured alien creatures similar to that used in Final Fantasy.
First, what you call 'Gaia' in Avatar is only loosely connected to the 'Gaia' concept as commonly presented - FF being a typical case. It is not some kind of bizarro living energy/soul that all life has an element of, it is instead a real *physical* connection between all living things. Avatar is really the first SF film to present such a concept (although it has occurred in SF literature once or twice before), so it should be applauded for actually showing is something new. (whereas FF was just recycling the typical 'Gaia' nonsense) ... Second, please show me a FF creature that looked similar to an Avatar one, I'd really like to see it. I have seen FF many times (and own it), so I am very curious.
But Cameron even stole from himself. Paul Reiser's character ... hard-assed female Hispanic soldier ... articulated mechanical thing
And? Cameron is hardly unique in recycling character archetypes. In fact, you'd have a harder time coming up with a director/writer who doesn't.
I'm fine with recycling ideas. I'm not so fine when it's done in such an overt way as to distract from the enjoyment of the piece.
So the film didn't grab you, like it did for many people. For most of us, the execution far outweighed the borrowed and recycled ideas. Again nothing new - That happens to all of us for various films.
But from your lengthy post, one also gets the distinct feeling (could be wrong) that you went into the film with a mental checklist of recycled items to look for. Again, that is your pejorative - but I wouldn't expect to get much enjoyment out of any film if I went into it with that mindset.
For example, I rented the "The Hurt Locker" yesterday. A very well-made film, but hardly an original idea in the whole film, or something not seen before. But it was well executed, so I enjoyed it a lot.
Speaking for myself (about Avatar), I was very affected by the film. I enjoyed the love story, liked the characters, and was transported to a world I hadn't seen before. That's what cinema is about. I'm sorry you did not connect with it that way...