Would it be possible to split into two sections: maybe an afternoon group and an evening group? Then you could meet at the same place, just at different times. The logistics of this would depend on what you do at your meetings, but it would give more people a chance to get involved.
If I was put on a waiting list at a guild, I would feel rejected, and go looking for a different group to join. A waiting list also sounds like a management/policy headache.