I took my Jeep out there for a day last summer. It's a blast, drove about 12 miles down the beach, saw lots of wild horses etc. There were few/no mosquitos on the beach but inland they were out of control - I made the mistake of driving down some trail and almost instantly there were 300 mosquitos in the Jeep with me. Somewhere there is some really funny videotape of me flailing around screaming while driving... In fact I think I remember hearing someone at the welcome center commenting on the fact that the mosquito population was so bad. (again this was last year, so ??)
I didn't see anyone actually camping *on* the beach... I know they had campgrounds, don't know how they work. I was strictly interested in driving out there and just hanging out for the day. Of course the pass to drive on the beach (for a year) was like $90. Also of course this isn't like Daytona, you drive on the beach only if you have a capable 4wd vehicle - and even a number of those get stuck. As far as I know you can fish/swim/etc wherever you want. I really don't know anything about camping - but if you just want to go to the beach.. make sure you hit Ocean City, just a few miles away.