You know, most likely you will be among dozens of people who aren't even slightly attractive. The hard-on issue is not really an issue. And I don't know about what kind of beaches you can dispose of, but there's usually women or families over there (unless, of course, it's a aknowledged as a gay cruising beach or similar.) And people stand put miles away one another.
That's at least what happens in Portugal.
I've already been quite a few times in nude beaches and I really enjoy it. 
But personally I don't see or feel a sexual part in it - it's just a bunch of people unprejudiced enough to enjoy their bodies and not have tan marks. 
Go there and look it up If it something starts to show, just roll over in your towel and hide hahah