Of course a lot of this is not possible but...if money was no object and I could do whatever I wanted...
Magic Kingdom:
-Turn the Swiss Family Treehouse into Tarzan's Treehouse and completely re-do it and make it more interactive and fun
-Re-do the Jungle Cruise's animatronics
-Have a permanent Jack Sparrow meet and greet next to Pirates
-Build a nice sit down restaurant in Adventureland
-Give Peter Pan's Flight a great update with better animatronics and effects
-Either completely re-do Snow White or get rid of it and put a Beauty and the Beast or Sleeping Beauty dark ride there
-Add an Alice in Wonderland ride to Fantasyland
-Get rid of Pooh's Playful Spot, build The Little Mermaid dark ride that was on the DVD next to Ariel's Grotto
-Add permanent Princess and Tinkbell meet and greets in Fantasyland (meeting in Fantasyland makes more sense than Toontown..)
-Get rid of the fair theme in Toontown and simply make it Toontown
-Retheme the area around the Tea Cups and Cosmic Rays and make a better entrance for Tomorrowland on that side (it's the one part of the park I don't think is themed well.)
-Get rid of the Speedway and use that space for a great new E-ticket indoor ride for Tomorrowland
-Get rid of Stitch's Great Escape and put a great new attraction there (completely gut it, don't just retheme Alien Encounter again)
-Give Buzz Lightyear a great update, change the guns (so they are more like Men in Black guns) and just refresh everything
-Keep Carousel of Progress but update it and continually change the last scene so it's up to date
-Give Space Mountain a big refubishment
-Add a great new daytime parade, keep Spectromagic but give it a great big refubishment and add better floats and more characters
Epcot:
-Get rid of Leave a Legacy and make the entrance to the park more beautiful
-Change the narration on Spaceship Earth back to Jeremy Irons
-Make the new ending to Spaceship Earth more interesting
-Either completely change Ellen's Energy Adventure or get rid of it altogether and build a brand new energy pavillion
-Put a really cool weather pavillion with an exciting e-ticket ride where Wonders of Life is
-Have a better themed Character Connection
-Add a third theater to Soarin
-Completely re-do the imagination pavillion. Keep a figment attraction but make it different. Get rid of Honey I Shrunk the Audience but put a new 3-D show there
-Add a cool white water rafting ride to Canada - but don't get people TOO wet
-Add some kind of Aladdin dark ride to Morocco
-Add a gondola ride in Italy
-Keep Maelstrom but re-do and make it longer if possible. Also add a seperate exit for people who don't want to wait to skip a movie
-Have more permanent meet and greets in World Showcase
-Add a nighttime parade
Hollywood Studios:
-Re-do the Great Movie Ride. Add more recognizable movies and get a new script
-Completely re-do the area from Indiana Jones to Star Tours
-Get rid of the Indiana Jones show and put an Indy dark ride there. Make it different from the California one (so it won't be too much like Dinosaur) but keep the same idea and make it different each time
-Completely re-do Star Tours and make an amazing new Star Wars ride
-Change the Honey I Shrunk The Kids playground into a Bugs Life playground
-Somehow make the Backlot Tour more interesting...have a different preshow, add more interesting recognizable props, spend more time in costuming (since it's the only somewhat interesting thing on the tour to me now) but keep the Canyon I guess
-After Toy Story Mania opens add more attractions to the Pixar section of the part. Maybe add a Ratatouille restaurant and an Incredibles ride
-Re-do the Voyage of the Little Mermaid theatre. Make the show a little more like the Broadway version and don't skip over half the movie. Since the show would be longer make it not continuous
-Move some animators back to Hollywood Studios and make the animation tour more interesting. Add more fun interactive things to the post show
-Have more meet and greets and add a Giselle meet and greet
-Make the Beauty and The Beast Show more like the Broadway version and re-do the threatre
-Add a great big two-story Broadway type theatre to the park and put the Aladdin show from DCA there
-Get rid of the Pocahontas scene in Fantasmic, use the Peter Pan scene instead. Also add more Princesses (Cinderella and Sleeping Beauty) to the Princess part
-In general, just try to better the theming of this park
Animal Kingdom:
-Add more animal exibits all around the park. If I don't go on the safari or walk the trails I hardly ever see any animal except for birds and maybe monkeys. I like how at Busch Gardens it seems like you see more animals
-Re-theme the Dinoland area (especially the Chester and Hester area) since it's the only part of the park that doesn't have great theming
-Add a Fantasyland-like dark ride based on an animated movie (maybe the Lion King, Bambi or Jungle Book? Something with animals of course..) I would probably put it in Camp Minnie-Mickey or Africa
-Add another dark ride but make it more like Pirates with boats
General:
-Expand the monorail to Hollywood Studios and Animal Kingdom
-Add a pirates water park