Good for you for knowing what you want. It's all too easy to say you want to go to a distant land and never truly determine what it is you want out of it. Not naive at all to want cultural experiences, at least not in my humble opinion. If all you wanted is to get smashed and make-out, why the hell would you pay thousands of dollars to do it in a foreign land? That's an oversimplification, but there's truth in it.

The party culture is everywhere if you look hard (and sometimes you don't have to look hard at all), Thailand seems to not be lacking in that department. I can't speak to the locations you mentioned specifically, but can say that if you find yourself in the middle of a moonlit beach party, enjoy yourself and don't forget that that may very well be a part of the culture too. Modernity marches on. Tourism. Globalization.

I'm embarrassed to say that I've never dived or snorkeled before...you'll have to inspire me there or else I'll just live vicariously through you :)