I think may claims, both positive and negative, tend to be exaggerated or cherry-picked. But I hadn't thought of some of the things you mentioned. It is difficult, however, to say which came first: acceptance of a certain degree of public nudity or large public nudity (or near-nudity) events like the bike rides, the mass nude photos, and body painting events. Naturally, there has to be a certain amount of interest in the first place to actually have a large scale event. But likewise, there has to be a considerable degree of tolerance to such things, too, which is going to be totally absent in some places I can think of. You'd never get away with a public nudity even in Lynchburg, Virginia. Naturally, that's true of a lot of things, like long hair on men, miniskirts, alcohol, drugs, divorce and so on. There is no logic to any of this, either. Jack Daniels whiskey is produced in a dry county where it cannot be sold, assuming you've heard of Jack Daniels or dry counties. Things do change, of course, slowly and nearly always surprisingly. For instance, when I was little, in the 1950s, condoms were nowhere to be found in stores but you could send a child to the store to buy your cigarettes. Today, condoms are for sale just about everywhere but you're carded (to prove your age) before you can buy a tobacco product.
The exact nature of the event and the behavior of the participants makes a difference in the effect of the event, too, as does who is actually participating. Even so, it's tricky. There has been a big motorcycle rally in Washington, D.C., for several years on Independence Day called Rolling Thunder. All-round reactions seems to have been generally positive, even with the image that bikers have. Who would have thought that would have happened? Body-painting usually seems like a festive event well-received, like a Mardi Gras parade, and the body exposure (to put it one way) seems to be a natural fit and it doesn't have to include plain, bare (and unpainted) nudity. If there are a lot of people taking part and there is no trouble, then it's a good thing and would help promote acceptance of public nudity--under the right circumstances. But the eternal questions will be, how many is a lot and exactly what sort of public nudity are we trying to have accepted. At the beach? Well, maybe, but downtown in the sidewalk cafes? You might say that's where push comes to shove. And all those videos of pretty girls walking around naked in public somewhere in Europe don't enter into the matter, no more than someone streaking a football game. But the East Woking Sun Club, people just laugh at that.