A film doesn't need "staying power" to still make a good attraction. A good attraction is good regardless and will still be fun long after any movie tie-in is irrelevant. How many people visiting Disney parks today have seen all of the movies most of the rides are based on or would consider them favorites that they watch over and over again? (Example: Carsland - Cars it the worst of the Pixar films - not counting the worse sequel - and yet the appeal of a Carsland is not diminished. Just because the movie was not great doesn't mean the land and rides won't be fun for more than just 5-10 year old boys.)
Avatar the movie was ok, but I was a bit incredulous since the entire plot is nothing but Pocahontas in space. It was visually very pretty, however, and if they can incorporate that visual aspect into the park space and ride(s) (which will be a must) then it could still be a cool place to visit.
I just hope they bulldoze the atrocity that is Dinoland USA in order to make room for it, though they'll probably tear up the Camp Minnie Mickey area instead and kill of FOTLK, which would be a shame, since FOTLK is the best stage show in Disney World.