Wow - how'd I miss this thread for so long!
I am not going to step into the fray, except to say that it is nice to see some pro-Avatarland support. I think the point is often missed in the argument that a great ride/experience can really come from anything at all. The example I always use is Splash Mountain - a fantastic ride made from a movie most people under 40 have never even seen.
Avatar has interesting (alien) environments and creatures from which to build an exciting ride. If allowed to do it right - and based on recent Carsland and FLE that seems to be the trend - Imagineers can make something great out of it.
Back on the main topic: as far as the Carsland argument goes - in concept I like the idea of DLR and WDW being different, but the fact is that the cross-over between the two is probably fairly limited. (My guess would be < 10 % of guests at WDW have been to DL more than once in the last ten years, and vice versa.)
Our family recently took our first trip to DLR this past summer. We enjoyed it very much, and would recommend it to any Disney fan to try at least once. However, I didn't think it was "better" or "worse" than WDW, just different. In general, I would say we will rarely go back there, though. More even because its so much harder to go to California than Florida, plus more expensive.
As far as Carsland - I am all for the duplication. RSR is an absolutely amazing ride, probably the best new ride to come out in the last 15 years. Something that good should be available to east coast residences (not to mention Europeans that are really unlikely to travel to the west coast for Disney). Having ridden it in California, I would love to see it in Florida.
I find the duplication of a more pedestrian ride like The Little Mermaid to be more disappointing. This ride is nice, but just a plain old dark ride. Why not one coast get Ariel while the other get - I don't know - Rapunzel. You can't be saving a TON of money duplicating this ride, right?
But, in the end, be it Avatarland, Carsland, Star Wars land, what I really care about (and you ALL should) is increased content in the parks. I want to see more/new stuff in Florida, and I'll take whatever they come up with. Even if I don't love it, if it spreads the crowds a little thinner, that's a good thing!
Anyways, that's my 2 cents.