My own Post of a Million Dreams:
Your mileage may vary.
MK - Tomorrow Land: I'm going to agree with the concept of going 50's retro here. Scrap Stitch, move Buzz to DHS (I'll talk about that in a moment), move Monsters Inc to DHS (or better yet, create that ride that should have been made from the doors scene.) I don't really think COP belongs here - but I can't really seem to bring myself to condone getting rid of it either. Maybe we could take COP back to it's original state that way we completely capture the nostalgia/Walt connection, and it lends it's self more to the idea of stepping into "the future that never was". Move the Racing cars over to DHS as well. The only thing I would keep in this area ride wise would be Space Mountain. Then add another coaster that captures the spirit of the original escape to witch mountain, I'll agree that this would be the right place to put Sci Fi Dine In.
MK - Adventure Land:
I don't know that I agree with making Aladdin a full out coaster ride but I think if we take it inside and combine a modern spin on old dark ride concepts, and pull the carpets along a track (maybe at coaster speeds, but with smaller dips and valleys.), and I think a new restaurant could work well here as well. Theme it to Neverland and at lunch have Peter and the Lost Boys character meet and greet, then do Tink and Faerie Friends at night.
A Pirates of the Carribian meal would not be a bad concept here either.
MK - Frontier Land: The only thing I can really think to add here is old fashioned gun fights by streetmosphere. (They do this at a place near where I live and it is a big hit with people of all ages.)
Ak: Make Rafeki's Conservation Station easier to find and reach. Add another show, sort of like Flights of Wonder - but using more animals in the act. Speaking of different merchandise in the parks, this would be a great place to sell those "adoption" kits where you pay like 20 bucks and sponser an animal out in the wilds. The money helps with scientific research, and the care of that animal, and in return you/your child receives monthly/quarterly reports on the animal that you have "Adopted".
Epcot - FW: First thing - get rid of the Future World Concept all together, the same issues that rise with tomorrow land and keeping it truly "futuristic" apply here as well. I'm thinking more a land of exploration theme.
Separate it out into 6 separate pavilions: Land, Sea, Space, the human body & the Mind
We already have the Land and the Sea
Space could include Mission Space, perhaps a small museum detailing the history of space travel, a small theater where you could watch the launches at Port Canaveral on the days when they occur, possibly even one of those large telescope like they have at conservatory and a shop where you could buy things like real star dust (we saw it at a conservatory once), and other space rocks, star charts, astronautic ice cream etc.
The human body was apparently covered once upon a time in Epcot so all we would really need to do is update and then bring that back into flow.
The mind could include the Imagination Pavilion, but also something that talks about how we learn, and the tricks that the mind can play on us (like why is it that if you ask 6 people who witnessed a crime, you get six slightly different takes on what happened?)
As for World Showcase? Before we start adding countries to that I would like to see them fix what they already have. They need at least one act for each country, unique (as in strip out every sign of Disney merchandise from this area of the park.) merchandise, I really don't see the point in adding rides to this part of the park (I know an unpopular opinion) because I really think it would mess up the theming of this section... if someone could come up with a ride that didn't just feel like "Gee somebody thought we needed rides back here so we just kinda shoved em in" I could live with that.
But my vote for first country to get added? Someplace in Africa, maybe Egypt?
I would also really really like to see a parade similar to Tapestries returned here.
Now for the one that really needs help on a massive scale: MGM
Divide the park into
Old Hollywood: Showcasing the original concept for the park (the Hollywood that never was), rides like the Great Movie Ride, lots of streetmosphere, the Brown Derby, those who hate the bricks at Epcot will hate this - but a Hollywood Walk of Fame where you can purchase your own star and become a legend in your own mind.
Pixar Land: Where all those rides I mentioned moving from Tomorrow Land can come to live. Re-theme the racing cars with the cars overlay and it slides right in. Lots of meet and greets with the Pixar characters (and this be the only place in the parks you can meet them... but then I think that should be done with pretty much everything but the fab "5", by limiting the locations where characters appear you open up to allow in a larger variety of characters and you make that section of the park more of a must do in order to meet these beloved friends.) I also think it would be neat if we could watch the animators work on the newest Pixar movies from here.
Disney Channel Live: Where (as someone mentioned before) one or two of the Disney Channel shows will be taped live, the Disney channel characters (like Kim Possible & Ron Stopable) can do appearances. High School Musical would also find it's home here.
One Man's Dream: Here we place attractions related to classic Disney Animation all the way up to The Frog Princess. Keep animation studios here (esp with the art classes), Make the One Man's Dream attraction the center piece and include a theater that constantly shows the really, really old black & white cartoons from Walt's day.
Now - Moving on I think it's time for a 5th gate.
One that would revolve around thrill rides and the villains. (If not this then they need their own section at DHS which could include TOT and a re-themed RNRC) This park would appeal to the Universal/teen crowd.
It would also be a good place to highlight works such as the new Alice in Wonderland and Nightmare before Christmas.
As for the resorts? I would like to see the Boardwalk built back up and more of the old entertainment added back. I think AKL needs some kind of special/interesting transport to AK seeing as how it is the only Deluxe that is completely stuck being bus transport. (Unless I'm wrong about this in which case - yay!)
For adult nightlife - I would like to see the return of PI but not without a real eye to themeing and story.
Anyway - that was fun.

As I said at the start, this is my dream - my if I could run the parks, had all the money in the world dream. I don't know how viable any of it is, I know that there are plenty of folks out there who will disagree with a lot of, if not everything I said... and that's ok. I just didn't want to miss this chance to play armchair imagineer.