Not sure about xmas eve as we usually arrive on boxing day but New Years Eve get down to the beach. We usually tend to abandon our evening meal or have something on the way back from the beach, then have a few drinks on the Candolim beach road from about 9ish and head down to onto the beach around 11ish. Great atmosphere, music, dancing, fire eaters acrobats etc and lots of fire works at midnight. Lots of the shacks have a bbq/buffet on which we did used to do but now prefer just moving around from shack to shack. Its a great night goes on for as long as you want it to. Found this year that some of the shacks drinks were hiked up a bit...I am sure we were charge 100 rups per drink at Spottys ( they have a good dance floor ) but for one night and a for the couple of drinks we had there it didnt make that much difference. Whatever you decide I am sure you will have a great time.
Just had a word with OH and he reckons that when we used to be there for xmas a few years ago now the hotels tended to put on a Gala night on either xmas eve or xmas day we never went to them so cant really comment but if your on a package it may be included in the price.