I believe that for WDW, there are two fundamental types of rides: Permanent and Temporary. There are some rides, classics, that could be there for a hundred years and still draw crowds and be entertaining. Space Mountain, Splash Mountain, Big Thunder Mountain, Tower of Terror, etc. The Big Ones. The rides you'll want your grandkids to ride.
Other rides and nearly all shows should be temporary. Temporary meaning they should have a definite lifespan, even if it's long. Snow White's Scary Adventures can go, rides at EPCOT need to be updated or gutted, and shows are cheap enough that they should be built knowing they're not eternal (with a few exceptions; hoop-dee-doo and luau...)
Some rides, Ellen's Energy Adventure for example, are fine and fun, but no one should expect will be around forever, even from its inception. I think WDW would do well to build this type of ride with an eye on how long it can realistically last before the space it's in can be put to better use.
I do get frustrated when I see rides that could have been eternal get shut down rather than updated. Superstar TV, I remember from my childhood, was a great premise; Pull up audience volunteers and recreate the hit TV of the day with a combination of theme-park goers and taped footage. They could build new sets every 3-4 years and maintain a good mix of classics and new shows. As long as there's TV, that could exist.
It's also surprising to see attractions who's heyday has long since past still running. Stitch's Alien Encounter thing, for one.
Disney would get a lot more mileage and more frequent visitors if they made steps to keep the permanent, timeless classics that might have time-sensitive material updated, and shuffled out the temporary stuff. It's cheaper to update an old ride than to build a new one. Cranium Command could have just had some new effects and film if it was too clearly 80's for modern crowds. The temporary stuff tends to be cheaper to build, and the idea of "there's a new ride" is a powerful draw, ESPECIALLY if people are being surprised by new experiences on familiar rides.
This has been a bit rambly, but what do you think? What rides have vanished that should have been timeless, what temporary rides have stuck past their expiration date? Is this too simplistic of a category system?