I suppose that Dracula, being an adaptation of the original book (and not the first; that was Nosferatu in 1922) has a get-out-of-jail-free card, as does the Charlton Heston Ben-Hur (, which was the third screen adaptation of the source novel). Great novels and plays can often be re-interpreted quite successfully.What about DRACULA? Lugosi's performance is timeless, but the movie itself had aged badly. And Christopher Lee proved there was always room for another take on the the Count.
(Edit: Blade Runner still doesn't need a remake,though.)
I don't know. I've always found the distinction between adaptations and non-adaptations to be kind of arbitrary. Most movies are based on something after all. I'm not sure why it would be okay to remake, say, LOGAN'S RUN, because that was based on a book, but not okay to remake FANTASTIC VOYAGE, which wasn't.
Matthew Broderick remade THE MUSIC MAN a few years ago. It wasn't bad, quite competent, actually. But it proved the point -- if you're going to re-make something basically the same as the previous version, what's the point? Broderick is a good actor, but c'mon -- this was Robert Preston's signature role. Make it your own, or don't re-make it at all. A lot of (good) musical theatre is probably like this.