I'm kind of a conservative guy, and my mood changes on this from time to time. I've never been a big fan of body modification. I don't like tattoos (they usually remind me of sidewalk graffiti, but even when they're artful it's not as bad but I think it's best to leave the skin unblemished). I used not to even like pierced ears (and I still think a girl wearing too many earrings is distasteful). My thinking was, "Why can't people just leave their body alone?"
On the other hand, whenever I see a girl showing off her belly-button piercing, it often looks cute and sometimes even sexy. It certainly looks much better than most other kinds of piercings people get, like nose and face piercings.
Then again, bare belly-buttons can look really cute as well. I think ultimately if you have a tummy worth showing off, it's going to look good regardless.
So ultimately, it's a toss-up to me. I think the answer is to go with whatever fits your style the most. If you like the idea of having it pierced, get it pierced. If it feels more comfortable the way it is right now, keep it the way it is. Whatever makes you the most proud of the way you look when you see yourself in the mirror is probably the way you should be.
Honestly speaking, it turns me on and I cannot control myself. I only like 3 types of piercings: Ear, nose and the belly button. If the belly button is cute and thin, a piercing keeps everyone's attention on it.