Well the thing is... Thundercats was a 3-5 year phenom while SpongeBob has been on the air for 15 years now
He's got a new movie coming out next February. I'd reckon he has a few years after after the movie which would make him a 20 year property.
When you've last 15 years or more (The Simpsons lasted 19 before Universal gave them a ride, Transformers lasted almost 30 years.
SpongeBob is similar to Mickey Mouse, Bugs Bunny, Mario, Pikachu, and Scooby-Doo in that even people over the age of 50 will likely recognize him if they are shown a picture.
That's why I would say SpongeBob, TMNT, and even My Little Pony have reached timeless status. Other kids shows barely last three years. To last more than 7 is remarkable and to survive over a decade is to be iconic.
I know I'd pay good money to walk through Bikini Bottom (Mrs. Puff's Boating School, the houses, Sandy's treedome, the Krusty Krab, Glove World, Jellyfish Fields, Rock Bottom, The Chum Bucket, etc) plus there's plenty of room for unique merchandise and attractions.
Fievel and Barney don't compare to SpongeBob because one only had two moderately successful movies and the other had a successful kids show that died off after 3-4 years (now it's just an average TV show)... SpongeBob was Simpsons popular in its prime. Even today, it's higher rated than a large majority of kids shows.
I'd like to see E.T. relocated to Hollywood, Curious George kept (he's timeless and a nice revamp of his area and possibly a small train ride or carousel could do wonders), Woody Woodpecker's coaster gets torn down for a nice, well-themed FAMILY coaster. Barney and Animal Actors can just be torned down as can Fievel - use the remaining unused nooks and crannies within KidZone and this area could be a solid place everyone can enjoy