"that seems like a perfectly reasonable compromise. It's what we've had to do with Morris sides - either offer a free limited festival ticket, which doesn't allow access to the mainstage events, or a reduced-price full festival ticket"
It has been discussed elsewhere, dancers - and traders - who are busy all day often only have evenings free. So a ticket that excludes the main evening events is absolutely useless.
Dancers and (relevant) traders are all part of the atmosphere. Without them, a festival is diminished.
I know at least one dance side which boycotts festivals that charge performers.
I also know Morris sides that really DO have bands of eight or ten musicians. Sometimes the musicians support more than one side. Perhaps the musicians should have to draw lots for the privilege of entertaining the festival's punters? Can't see it working, somehow.