Hello, Alison!
My almost 11-year old went through a similar change of heart before our last Walt Disney World vacation. I know what you are feeling - my Disney heart was almost shattered into pixie dust! Our first couple of days were still wonderful, but I knew he wasn't having as much fun as he could be. After talking with him, he admitted to me that he was worried about looking 'silly' or what other kids his age there would think of him. After we explained to him that he will never again see any of those other children and even mom and dad act like kids at Walt Disney World - he loosened up and his Disney Side was out in no time!
Now that he is older, my son really enjoys the rides. His favorite rides at Magic Kingdom Park are Splash Mountain, Space Mountain, and Big Thunder Mountain Railroad. At Epcot his favorites are Test Track Presented by Chevrolet, Mission: SPACE, and Soarin'. Your son can also design and then 'ride' his own thrill ride at The Sum of All Thrills located in the INNOVENTIONS East building. He also likes Rock 'n' Roller Coaster Starring Aerosmith, The Twilight Zone Tower of Terror, and Star Tours – The Adventures Continue at Disney's Hollywood Studios. And finally, at Disney's Animal Kingdom Theme Park we can't miss Expedition Everest - Legend of the Forbidden Mountain, Kali River Rapids, and DINOSAUR.
My son also loves the food! If your son is adventurous - Walt Disney World is a great place to try new foods that you wouldn't have an opportunity to have at home. The best place for this is Epcot World Showcase.
As you already know, there are many things he will love at Walt Disney World Resort. There is something for all ages. It is true that he may have, at least for now, grown out of some things - but there is so much more to Walt Disney World than some of the rides and attractions geared toward younger children (though I still go on those each and every time).
Have a magical day, Alison!
~Rachel