As someone who was acting as an usher at a Bert Jansch concert a few years ago where he kept cranking the level of his instrument up himself, forcing the sound techie in the box to follow suit with everything else, I and quite a few of the audience could have done with earplugs.I could feel the vibrations through the floor via my feet (and everything else) sitting at the back, and even with attempts to block both ears with fingers it was still fearsomely loud (and not much fun with the tinnitus I suffer from either). So nothing wrong with earplugs. (After all a fair few musicians at our venue during the week wear them while performing - and I do mean earplugs and not in-ears).

As to dancing in the aisles, that is generally a Health and Safety no -no,and normally subject to the rules of the venue, not the Folk Police. (For instance the forthcoming Belloowhead in the spanking new arts venue 1000+ seater in Guildford will be a seated only gig, and I have no doubt that will probably be down to a mix of need for specific number of bums on seats and the Health and Safety regs.