As much as I hate to admit it, it seems like nothings sacred in Walt Disney World
If Walt Disney was alive today, he'd remind us we always need to keep moving forward. The park is not and was never intended to be a museum to itself. When Disneyland and WDW opened, they were showcases for the most imaginative, inspiring and technologically advanced entertainment possible at that time. When a ride is no longer particularly imaginative, inspiring, or technologically wondrous, it should be updated or replaced. It's NOT enough for a ride to bring you nostaglic warm feelings.
* Mr. Toad was a simple "funhouse" type ride using 1950s-era technology. Pooh is an upgrade in almost every respect and is enjoyed more by young children today who know and love the characters.
* 20K was groundbreaking when it opened, but it became less exciting as the years went by. I never experienced crowds there in the early 90s, even at peak times. The ride itself required so much maintenance that it just didn't make financial sense for them to keep it open. For most people, it is not missed.
* I remember Horizons very fondly. However, recently I found a video of the ride online and found it surprisingly boring - almost preachy. It was actually a fairly long ride. I only remembered the coolest parts I guess! Plus the building was literally falling down and I don't think repairing it was possible (or at least financially reasonable.) In any event, Mission Space is a tremendously exciting ride, using technology to amaze and inspire us (as long as you don't barf).
* Wonders of Life is a great concept. I hope Disney gives some thought to it, there is so much emphasis on healthcare in our world today I'm sure Disney could get a good sponsor for the attraction. But the whole thing would need to be redone - Body Wars made more 3D, more immersive. Making of Me scrapped (cute but so outdated, and a difficult concept to execute), Cranium Command redone in some way to allow more audience interaction and/or participation, or just scrapped in favor of a different health-based attraction. There's so much they could do about taking care of your body, living longer healthier lives, etc. Disney spends so much time talking about the power of the human spirit.... this pavillion could look at what happens when the human spirit is directed toward the human body.
* Delta Dreamflight was a fun ride, but Buzz Lightyear just BLOWS it away. Not even close. And while your point about Pixar movies eventually getting dated is valid, Buzz is so well executed that it will continue to be popular long after "Toy Story" is forgotten. In fact, it will be a sort of trivia question, like "What movie is Splash Mountain based on" is today.
* Mission to Mars was THE single worst Disney ride I've ever been on. For those who don't remember, you sat in a circle. A voice announces that you're on the way to Mars and the floor and seats vibrated. The technology was so rudimentary. The concept was essentially the same as Mission Space but the execution is not even in the same league. Now I'm no great fan of Stitch (I preferred Alien Encounter), but the execution is kind of cool and the younger kids seem to really like it.
* I think you may have a point about Timekeeper vs Monsters Inc., as Timekeeper was a great show. But the thing was practically empty. Nobody knew what it was, there was no compelling reason for anyone to ride it. Interestingly, I think the technology used in Monsters works much better in Turtle Talk with Crush. But Monsters usually has a good crowd and Timekeeper didn't. So it's hard to argue with that.
* The Carousel of Progress is one of my favorite Disney rides. But even I can see it's outdated. It needs a MAJOR rehab at minimum, or perhaps better still a total reworking of the concept to make the experience more immersive and involving - maybe go outside the kitchen to truly experience what life is like in 1900. Drive into town! Wouldn't that be cool?
I've said for years that Disney should create a small attraction showing the history of WDW - old photos/films of the parks under contruction, interviews with Walt, Roy and others involved in the creation of the parks, etc. For a time they had something like this in the "Town Hall" building inside Magic Kingdom's entrance. Maybe they could even set up some kind of virtual reality thing where you could "ride" World of Motion, Carousel of Progress, Mr. Toad, 20K, Horizons, Dreamflight, Mission to Mars, Captian EO, etc. and even cartoon-generated "rides" of attractions that were planned but never built!
I think no matter how we feel about these rides, most of us here would check that out!
Jon