I was lost during the years I camped with ESD (big at either camp, 35-50, maybe) but some of that was being the wife, not the emt. I do fairly well in the ~30 size of the Booby Bar, but I think that's also due to interacting with the core group on line all year. And we are part of a village, so that brings me to a larger, yet still accessible group. (<150, I think)
For me, it's not the size, but the people. I'm an introvert, so it really helps that I have a place that I can retreat to and to have people I trust nearby. It may help to think of not the advantages to joining a group but of the work you'd owe the place and the amount of autonomy you want.
Simon's real sig line?
Embrace the Sock
Winners never quilt, quilters never win...