First time we went, I brought a little black dress and a few other evening pieces just in case we went out for a fancy dinner. They didn't even make it out of the suitcase. If I want to wear something that makes me feel dressed, but not overdone, I throw on a sarong w/matching top and flip-flops.
Maybe it's just my hippie tendencies, but I'm perfectly content in shorts & a t-shirt in any restaurant down there. (Gee, sounds a lot like Denver...really laid back.) The only make up I bring is lip-gloss & mascara. Anything else makes my skin too oily with the humidity. As far as jewelry goes, I leave my wedding ring and fancy pieces at home and trade them for a simple band & hoop earrings. I would just die if I lost RobertE's grandmother's ring!
I try and go for the casual-cute look rather than the club-cute look. The warm weather and the fabrics used in most club clothes will only make you sweat more. Think light & flowy and you won't go wrong.
If all else fails and you'd rather not trust the input from complete strangers, you can do like the rest of us...bring what you're comfortable with and you'll learn what works best for you for the next visit.
After four visits, I think I've scientifically gotten my wardrobe down to what effectively fits in a duffel bag for a 10 day trip.
This makes the Mr. quite happy.
Good luck and have a wonderful trip.