I've done the World Naked Bike Ride a couple of times and I've visited a nudist beach occasionally, but I'm not a hardcore nudist or anything.
But for what it's worth, erections are a non-issue for every nudist I've spoken too. No one really cares.
And I wouldn't say someone naked is any more off-putting than someone in a too-tight swimsuit, even if nakedness WAS for the benefit of any on-lookers (which it obviously isn't).
I'd urge everyone to be comfortable with the body they have, and if you want to go naked, why not? I wouldn't let shame stop you.