Not sure what sort of experience your up for, but if you really want to spice up the nightlife of your dive/camping trip--and do it very inexpensively, consider Jabour's campground, which is the ONLY campsite on Key West proper, and literally a 2-minute walk to Duval St. You could drive the 1/2 hour or whatever to better dive sites. Jabours is entirely RV's, but I'm pretty sure they'll let you pitch a tent under a tree. I did so my Sr. year of college for a VERY low-budget spring break. You can imagine what the tent smelled like after a week of 3 guys living in it, but all-in-all it was a blast. Too bad I didn't dive in college!