David
I am not trying to contradict you,   especially if people pay to come there, I think an open mike with a limited amount of time is good for those folks. I hear what you are saying... I have been to places where someone really really bad wants to play for an hour. That is why when people pay they it should be people who have been reviewed and approved and think there is nothing wrong with that at all.

On open mike night, let them play but limit everyone to a song or two unless the audience wants more ..
that would be my solution ...