You make very good points, Steve.
I have much more experience with informal jams in somebody's home or backyard than in a club setting where somebody has control of the agenda and the mixer. I don't own an electric guitar (my Guild has all the on-board electronics I want) and I often jam with other musicians who have electric guitars but none of the instruments is run through mixing board.
My main beef has to do with the level of amplification. Please don't overpower the other musicians. One of our friends may not be invited to our biggest jam because of his penchant for plugging in his Dobro, cranking up his amp and over-riding the moods or rhythms that the lead musician is trying to set.
Bob