I don't have any problem with this the vast majority of the time. I regularly rewatch films, simply because I enjoy watching films. I like noticing other stuff in the middle I didn't see before. I like thinking about whether they're foreshadowing the ending, or whether knowing the ending changes what earlier scenes mean or how they appear.
Yeah, enjoying movies I've seen more than once isn't usually a problem for me. Actually, if I'm being honest, some of my favourite movies are ones that I didn't really appreciate until the second or third time I saw them, and picked up on things I'd either missed or not really thought about the first time.
Generally, I take the view that if I can't sit through it more than once, it's probably not a very good movie (or not an entertainingly bad movie).
Admittedly, there is a serious problem that appears in prequels, and that's where you know where the events lead to, but the prequel itself doesn't make any sense in that continuity. That's annoying as hell. Knowing that a character is going to grow up to be evil or whatever can lead to a really interesting, tragic tale. But, done badly, it can completely undermine the credibility of the story it's trying to set up, either by undermining the characters we're interested in, contradicting events we know to have happened, or just by being flat out stupid.