If you look in the disABILITIES FAQs thread, in post #3, there are links to the official WDW Guidebook for Disabilities for each park. In those, you will find a list of attractions with an icon for each one that tells what the access is (must transfer or can stay in the wheelchair).
This is a complete list of which attractions you can stay in a wheelchair for and which require a transfer:
Magic Kingdom® Park
Can stay in a wheelchair or ECV:
Ariel's Grotto
Castle Forecourt Stage Show
Country Bear Jamboree
Donald's Boat
Fairytale Garden
Frontierland® Shooting Arcade
Galaxy Palace Theater (seasonal)
Judge's Tent
Jungle Cruise
Liberty Square Riverboat
Mickey's PhilharMagic
Mickey's Country House
Minnie's Country House
Monsters, Inc. Laugh Floor
Shrunken Ned's Jungle Boats
Toontown Hall of Fame
"The Enchanted Tiki Room Under New Management"
The Hall of Presidents
Tomorrowland Arcade
Walt Disney's Carousel of Progress (seasonal)
Guests in motorized vehicles, ECVs, must transfer into an available wheelchair at these attractions (if you are already in a wheelchair, you can use it in the attraction and won't need to transfer:
Buzz Lightyear's Space Ranger Spin
"it's a small world"
Stitch's Great Escape!
The Magic Carpets of Aladdin
The Many Adventures of Winnie the Pooh
Tom Sawyer Island Rafts
Walt Disney World Railroad
Attractions requiring Guests to transfer from their wheelchair to board the attraction include:
Astro Orbiter
Big Thunder Mountain Railroad
Cinderella's Golden Carousel
Dumbo the Flying Elephant
Mad Tea Party
Main Street Vehicles
Mad Tea Party
Peter Pan's Flight
Pirates of the Caribbean
Snow White's Scary Adventures
Space Mountain®
Splash Mountain®
Swiss Family Treehouse - Guest must be ambulatory
The Barnstormer at Goofy's Wiseacre Farm
The Haunted Mansion
Tomorrowland® Indy Speedway
Epcot®
Guests may enter and enjoy these attractions in a wheelchair or ECV:
Mexico: Art of Mexico Gallery
Japan: Bijutsu-kan Gallery
China: "Dragon: Ruler of Wind and Waves" Gallery
China: "Reflections of China"
Imagination: "Honey, I Shrunk the Audience"
Imagination: Journey Into Your Imagination with Figment
France: "Impressions de France"
Innoventions East & West
Canada: O Canada!
Norway: Stave Church Gallery
The American Adventure: The America Gardens Theatre
The American Adventure: The American Adventure
The Land: The Circle of Life
The Seas with Nemo & Friends: All Attractions
Morocco: "Treasure of Morocco"
Guests in motorized vehicles, ECVs, must transfer into an available wheelchair at these attractions (people using a wheelchair may stay in the wheelchair):
Universe of Energy: "Ellen's Energy Adventure"
Mexico: Gran Fiesta Tour Starring The Three Caballeros
The Land: Living with the Land
Attractions requiring Guests to transfer from their wheelchair to board the attraction include:
Norway: Maelstrom
Mission: SPACE
Spaceship Earth
Test Track
The Land: Soarin'
Disney's Hollywood Studios
Guests may enter and enjoy these attractions in a wheelchair or ECV:
ABC Sound Studio
"Beauty and the Beast" at the Theater of the Stars
Disney-MGM Studios Backlot Tour
Fantasmic!
"Honey, I Shrunk the Kids" Movie Set Adventure
Indiana Jones Epic Stunt Spectacular
Muppet*Vision 3D
Lights, Motors, Action! Extreme Stunt Show
Playhouse Disney - Live On Stage!
The American Film Institute Showcase
Voyage of the Little Mermaid
Walt Disney: One Man's Dream
Guests in motorized vehicles, ECVs, must transfer into an available wheelchair at these attractions:
The Great Movie Ride
The Magic of Disney Animation
Attractions requiring Guests to transfer from their wheelchair to board the attraction include:
Rock 'n' Roller Coaster® starring Aerosmith
Star Tours
"The Twilight Zone Tower of Terror"
Disney's Animal Kingdom® Theme Park
Guests may enter and enjoy these attractions in a wheelchair or ECV:
Caravan Stage: "Flights of Wonder"
Cretaceous Trail
Conservation Station
Discovery Island Trails
Finding Nemo - The Musical
Fossil Fun Games
It's Tough To Be A Bug
Lion King Theater: "Festival of the Lion King"
Maharajah Jungle Trek
Pangani Forest Exploration Trail
The Boneyard
TriceraTop Spin
Wildlife Express
Guests in motorized vehicles, ECVs, must transfer into an available wheelchair at this attraction:
Affection section in Rafiki's Planet Watch
Kilimanjaro Safaris
TriceraTop Spin
Attractions requiring Guests to transfer from their wheelchair to board the attraction include:
DINOSAUR
Expedition Everest
Primeval Whirl
Kali River Rapids
For the question about Soarin', if you go to page #2 of the
Epcot FAQs thread, you will find some ride pictures, including some pictures of Soarin'. I don't have any that really show the height of the seats very well - without people in the picture, it's hard to get perspective. My memory is that they were lower than my DD's wheelchair seat - the top of her seat is 23 inches from the floor. I seem to remember the Soarin' seat more the height of the bottom of her wheelchair seat - more like 17-19 inches.
My DD can't lift herself, but she can stand if we lift her up. With the wheelchair parked right next to the ride car, Soarin' is one of the easiest transfers for us to do with her.