I'll go with Jon's advice on booking acts that have a sense of passion for what they're doing. I can't think of any reason for booking anyone who doesn't!

Greg B, you said, "Egalitarianism. Festivals are not concerts. That means 'performers' are expected to arrive by the advertised opening times and leave not before the end of the 'closing concert.' And they're not to hide off in the corners, or in their hotels, or run off to another booking in the middle of the event. They're to be in for the long haul. They're to eat with 'the rabble' and live in similar quarters, show up to sessions and sing-arounds. If they're too 'important' to do any of those things, then they
ought not to be paid to be at a festival."

That's all very well, but festivals in this country frequently book, at great cost, a number of 'big-name' acts for one concert each, so if you miss that concert, you miss that act. This, I believe, at the expense of the sort of acts that would happily do exactly what you are asking for. It never used to be that way, but that's certainly the way it seems to have gone in recent years.

Barbara