Communities need boundaries to exist, but too many rely on registration to distinguish between "us” and “them”. Your boundaries need to be tougher than that. If there was no registration, how would your members know who was in or out?
Living in your neighbourhood does not make you a member of the community. Knowing the postman’s name, attending local events and talking to your neighbours does.
Your community's boundary might be simple, like participation. It might be profitable, like buying the latest iPhone. Or it might be attending an industry event, befriending a considerable number of members or writing a thought-provoking post.
You can create groups for, identify and highlight the people (both new and old) are are crossing these boundaries.
You also have to make a decision. You can pick an easy boundary, gain more members and have a weaker community. Or you can pick a tougher boundary, have a stronger community, but with less members.