I want and don't want a Simpsons expansion...
On one hand, a Simpsons expansion sounds great because that area of the park is disjointed in theme. You've got the Simpsons ride with a Kwik-E Mart and all those differently themed eateries. Back to the Future (going away, I guess), the Flintstones, El Pollo Loco, Mexican food, Italian food, etc. Expanding the Simpsons in that area would unify the theme more.
On the other hand, although I'm a fan of the ride, the Simpsons aren't my favorite. I won't deny the hilarity of the Simpsons, but I would prefer something else.