I'm sorry to sound nitpicky, but you can't say "these lands were based solely on..." and then proceed to list 3 or 4 direct influences. "Solely" would be if they were like the current developments, entirely based upon a single IP; if they're based on 3 or 4, then they're being influenced by an entire genre, albeit genres that Walt Disney Productions were certainly emphasizing in the mid 50s, as you indicated.
I agree with what a few others are saying here: the key, in my book, is to ensure that you never unnecessarily limit yourself from a creative perspective. Yes, any land that's developed requires theming, and theming in and of itself has a slightly limiting quality (e.g. not every concept can fit into Frontierland, or Future World, or Harambe Village, or Sunset Boulevard), but most of the lands Disney has developed up to this point have minimized the risk of limitation by making their themes quite broad and expansive. Lots of people can understandably ask why the MK Haunted Mansion is located in Liberty Square, but all it took back in '71 was some smart architectural theming by WED Ent. and, next thing you know, it blended right in.
Something like Avatar Land presents a big risk in this regard. While we're all hopeful that it turns out great, and while I'm sure there'll be some wonderful aspects to it, James Cameron's Avatar is simply not a red hot property, and it's questionable if its forthcoming sequels will propel it significantly back toward prominence in the public eye. If Avatar winds up being a decently successful but by and large unmemorable film franchise, then the themed area's relevance is given an unnecessarily short shelf life. This presents a potentially big problem should a retheme become necessary, though I've been thinking from the start that Disney is likely going to build this land in such a way that they can give themselves an out on it should they ever want to retheme. Still, there's the potential for the creative process to be hamstrung by a film franchise that as of now is no guarantee to be particularly popular over the next decade.
Star Wars Land presents a different challenge. Given that the franchise is about to hit its 40th anniversary and has a few more films in the immediate offing (and a very successful recent installment), it clearly has the legs, the cross-generational appeal, the rabid fanbase, and the relevance to support an entire themed area, much the way Potter works in Universal. However, it too also carries the possibility of unnecessary limitations from a creative point of view; I'm fully aware of how expansive the Star Wars universe is (I still have my old, mid 90s copies of Timothy Zahn's Grand Admiral Thrawn trilogy packed away), but any attractions, rides, or architecture you create must be influenced by Star Wars and Star Wars alone. While I think SW Land can have better staying power than Avatar Land, it's still more limiting than something with a broader theme, like a Sci-Fi land (1994 Tomorrowland?) or the original concept of Beastly Kingdom.
None of this is to say those areas are going to be failures, far from it, but it's my opinion that adding layers of unnecessary creative limitations as a rule of thumb rather than as an exception for a major property like Star Wars is an ill-advised direction to follow long term.
