If your community had a waiting list, what would it be like?
Have you considered creating a 1 in 1 out policy? Each month a few dormant members of the community are removed and the community gets to choose from a list of applicants.
Each applicant gets to provide a few details about themselves, what they would bring to the community and explain why they should be chosen.
This would work especially well in tight communities, with paid subscriptions with less than 150 members.