A couple of years ago there was a bit of a spat between this site and the geocachers' site. No, lets be honest, a full scale flame war. I've an idea it resulted in them changing their rules. And it definitely caused a change to the Megalithic Webmasters code on visiting Ancient Sites which now specifically says don't leave caches.
On the subject of Julian Cope's attitude, I don't think he is a conventional conservationist as such. He seems to revere sacred landscapes as much as the sites themselves and is big on seeing the sites for their present value as much as their original form - even talks of it being OK to re-erect and re-arrange stones to suit modern people's needs, like ancient people did, and arranging wind farms into circles. If its "modern use" that is the most valuable aspect in his view I suspect he'd approve of climbing on them and leaving offerings and geocaches - though that's just my guess.