Richard, I know you're on the side of the folkie, sometimes I just cavil at your way of expressing it! I'm sure your heart is in the right place.
As you may have noticed, I've run singarounds/ open mike sessions over the years as requested and now think that the session in which all present join in as often as possible right through over say a two-hour span is the way I like to go- purely personally- as there seems to be a shared understanding, a swelling of mutual sound, a harmony, which doesn't automatically arise where individual performers do slots.
In sessions like this, it's the host's part to ensure that everyone gets to lead fairly, that other performers accompany sympathetically and that ( the part I particulary enjoy) there is a balanced variety of music and song throughout. In my experience it's quite rare for that to arise spontaneously- often the ablest performers take things away from the others at their pace. The very best, of course, are usually pretty generous in helping others along if the session is set up and explained beforehand... think of CT or SM or CS or KK or Liam Robinson in this respect...
So we all have our preferences, and will find venues suitable- and at the end of the day, if we find ourselves in the auction room with an unsold lot, may reflect that we just didn't bring what people wanted to take home with them... any more grizzled philosophy comes in my slim volume 'Life, 6 Chords & A Capon'.....
Bob