No flames here, just thoughtful discussion of the issues. For the most part, obvious examples such as 20K and Mr Toad notwithstanding, Disney seems to have done a pretty good job of hitting that balance between keeping the classics and adding the fresh stuff. Can you imagine the outcry if Its A Small World were ripped out and replaced with something from a new, faddish film? (Just an example, I personally despise that attraction). So Disney balances it all out, sometimes they make mistakes, but usually they do pretty well.
Universal, on the other hand, seems to have ignored that equation completely. Need a new thrill attraction? Why not house it in the old Nickelodeon building, which is currently empty 90% of the time, except when pressed into service once a year as costume central for
HHN? Why not put SOMETHING, anything, in the old Murder She Wrote theater that's been empty for years?
Having worked for Universal off and on since 1992, I've got a fair idea of what the "classic" attractions are/were: Kong, BTTF, Jaws, ET, Hitch. I'd add the original Earthquake to that list, though it's been so long since it was what it was designed to be, I doubt very many even remember its glory days.
That leaves an awfully long list of updatable attractions. I personally think it's criminal to have changed Hanna-Barbera to Jimmy Neutron (a classic to a fad), but I can understand the reasoning behind it. And in that case, all that was really altered was the film. The ride itself was tweaked but not destroyed. And I'd be willing to bet that somewhere in the Universal vaults resides the original film, just in case the Neutron fad crashes and burns. The Beetlejuice Graveyard Revue is another excellent example of updating without destroying. Although some of the incarnations have been awful, others have been well-done. That show is constantly revamped in an effort to keep it new, but without sacrificing what us old-school fans have come to expect. Same thing with the Horror Makeup Show. I'd be crushed if it went away, but I love watching the constant evolution. Same thing with Animal Planet Live, which replaced Animal Actors.
Some things can, and should, be shut down permanently to make room for others. I loved the old Murder She Wrote post-production show, but the series didn't become a "classic" in that sense. I'd love to have seen it revamped and based around a new property, but I understand that modern audiences don't care so much about how editing happens. Shutting down the Wild West Stunt Show and using the theatre for Fear Factor was brilliant. Same concept, new branding/audience participation element. Awesome.
So in essence, my opinion is that there is plenty of room for Universal to update/revamp/add on, but they need to keep an eye towards their audience. A big chunk of their audience are loyalists, who have been avid fans since the beginning, and getting rid of everything we held dear is not the best way to retain us, or encourage us to bring our kids into the parks.
Just my opinions, of course.
and I used to watch Simpsons all the time.....but, my gut tells me Simpsons....or, at least something "family" and not "thrill"...... 
....i was thinking Jaws was next on "hit list", but if they already closed ET in California.....uh-oh.....
