I don't really agree. It's like saying a bad movie of a great book ruins the book. It doesn't.
When the author James M Cain (postman always rings twice, etc) was asked by an interviewer what he thought about the films that had destroyed his books he pointed to his bookshelf and said: "They didn't. My books are still there".
Never heard a good remix or a cover either.
It could happen I guess with some neglected or underrated song with a different take.
Are you talking just Smiths songs here, or songs in general?
You've never heard a good cover of a song? I can't think of loads of great covers.