We like Caye Caulker also but we visit Caye Caulker for a day trip each visit instead of staying there. Much more to do on Ambergris. I think if you stay there and just visit Caye Caulker you'd have more fun esp. as far as night life goes. Ambergris frequently has "block" parties on the weekends which bring out a lot of folks and have a very festive environment.
We'll be back starting Wed of next week. When will you be there?