I think having the 2 park split, plus a more 'thrill' oriented park with Studios is a great opportunity to keep DLP as a lighthearted 'European' halloween, keeping it traditional and quaint, and then using WDS as a more intense halloween, with movie villains/monsters roaming the park as if they've broken loose from their movies.
That way you can have 2 halloween events for guests to visit, and no one has too much of a visit affected.
I do like the idea of changing Adventure Isle to something though, I think it's been missed as an opportunity. If not zombies, then definately having the moonlight skeletal Pirates from PoTC Curse of the Black Pearl roaming the area. It'd tie nicely with the area and add an extra for halloween.