The open pool sessions do pretty well. We average about 10-15 people, although sometimes we have quite a few less, or several more. It can depend on weather, how close to the season we are, holidays, etc...
For polo, like jeff said, we usually have enough for at least two teams. That's about 10-14 people. Back in the day, old timers talk about 20-40 people showing up. This allowed for different leagues, including a women's league. For as much fun as it is, I'm surprised the bubble burst. I think a lot of them got old, had kids, or moved away. If you have never played polo, come out and try it! It is super fun and is a great way to stay in paddling shape.