I went to a nude beach once. I was sitting near a guy who was lying on his back. He was watching me take off my bathing suit and he got an erection. I couldn't believe how hard he got. It stood straight up. I didn't find it offensive. It was actually flattering. He even came over to talk to me. The entire time his penis was standing straight out. I enjoyed seeing him excited.
I have been to nude beaches before and I ahve seen pleanty of erections at those beaches and sometimes it is sexy but most of the time it's really not. The one time it was sexy was because it was just my fiance and me ;)
It's not sexy, this to me says "I'm only on this beach to get off because I can't get it any where else" not hot. I haven't been on a nude beach before but I'm sure it's for the purpose of being comfortable with your sexuality and feeling free, one with nature etc, but not one big orgy. I'm not saying you won't get aroused by naked bodies but, if your going to go to one you need to have control over your member.