One of my buddies who is a singer down South joined a church choir as they had a member who was a vocal coach and gave lessons for free to choir members.
Locally we also have a community chorus and local theater troupes. I always have an eye on those.
IME the open mikes never helped me with band networking, I found that most of the performers were either pretty average, or not interested in band situations. A lot are only used to accompanying themselves, I have seen a lot of timing issues when you play behind them, and complaints about that I'm off. Often, with a locked up drummer no less.
Also, many are solo performers interested in doing only their own material, BUT, around here the musical community is small and it doesn't take all that long to get the word out amongst them, I did find OM's useful for that.