Well I haven't been to wdw recently so my list may change when I get back but I would add 2 countries to Epcot World showcase.
1. Greece- I would build a roller coaster/ dark ride of Hades underworld. A greek quick service place that sells gyros and goodies, and a nice greek table service place. character meet and greet with hercules and megara. It would also have a musical stage for Hercules the musical.
2. Brazil- a nice brazilian steakhouse, a new Carnival parade, a water ride based loosely on the Emporers new groove set in
amazon jungle.
Hollywood studios would get 3 new restaurants. One would be for character dining with the muppets, one for character dining with star wars characters, and a new quick service food court.
In Magic Kingdom I would add a new 3d movie, a 101 dalmations cruella de ville dark car ride, and a new show in Frontierland. New character dining at Tonys Town Square with Lady and the Tramp and Pinnochio characters.
In Animal Kingdom I would add with 2 more kiddie rides. One based loosely on the Jungle Book and the other on Tarzan. New Tarzan character meet and greet. I would add a forest section with a new fox and the hound ride, and bambi character meet and greet. I would add an Aussie land with more animals and offer a walkabout experience through the outback.(kangaroos, kolas, etc). Character meet and greet with characters from the Rescuers Down Under.
I would also do the mythical creatures land that was orignially proposed. It would have a medieval theme featuring dragons, unicorns, centaurs, etc. There would be tie in to movies like Sword and the Stone, Sleeping Beauty, Pete's Dragon, Brave, and Robin Hood. It would also have a castle with a nice restaurant. There would be a experience for boys like Jedi Training academy where they turn into knights and prices and learn to fight to slay the dragon.