Here's what I'd do:
1) I would add 5 rides to Hollywood Studios so that it would be more of a full-day park.
2) I would do the same to Animal Kingdom.
3) I would update Tomorrowland, starting with the Speedway. First of all, in its current incarnation, it has nothing to do with "tomorrow." If they can't make it futuristic, then perhaps it should become part of another land.
4) I would add at least one more country to Epcot. I can't see why this hasn't been done already. They are all money makers to the extreme -- just stores and restaurants. Give the people what they want!
I think the highest priority should be placed on adding more rides to Hollywood Studios and Animal Kingdom. Although I like some things about each park, I can't handle more than a few hours at either one. If there were 5 more rides at each, I would consider making a day of it.