About dressing up on holidays - Tourists tend to be the ones who don't dress up. Belizeans and other residents will definitely take the opportunity to dress to excess with glitter, spandex, sequins, etc. (at least for the ladies). If you are considering Mata Chica for New Year - definitely dress up - the flashier the better actually. There are a lot of places for women to buy such outfits right here on the island - suggest stopping in at Mambo Chill for some super fashions. For men - a nice shirt with buttons and clean shorts with a belt will be considered dressy enough.