I actually think Spongebob is deserving of a land. It's got the staying power, seeing as I'm 20 now and watched it when I was young and my little sister (along with every kid at her preschool) watches it and loves it now. It also has tons of content to replace KidZone with; Krusty Krab, Glove World, Rock Bottom, Mrs. Puffs Boating School, Shell City etc. Spongebob could also replace E.T. with a ride that takes place in Bikini Bottom. It makes the most sense IMHO. Also the overlay would actually give KidZone some identity and cohesiveness, which I think it lacks in its current state.
I mean think of all the food options the Krusty Krab would present, you can't tell me you wouldn't love to taste a REAL Crabby Patty (though the name is unappetizing)