I was going to mention Gambridge as being simply a big concert and not a festival at all; but a quick look at their website shows that they now encourage sessions and "fringe" events, so there's hope yet!

GuestGuest
I didn't mention monetary consideration at
all, did I? Though if everyone is camping
the farmer will like a handshake!
If premises have to be rented for
workshops, of course there must be a
charge.
If the organiser decides there should be
concerts, again there has to be a charge.
My point is that neither workshops nor
concerts are essential to a festival. And
the day a festival is only judged on
whether it make a profit will be a really
sad day.

As I've said elsewhere, many musicians provide welcome entertainment outside of the main festival venues, at their own expense; for members of the public, who can join in singing their own favourites, can have the basics of different instruments demonstrated; frequently the public, and their children, are allowed to try different instruments. Not to mention that we pay exorbitant festival week campsite fees; And for this you call us freeloaders and parasites?