I think having a members only area could be useful, we have that on both my own forum and the metal detecting one I admin. GC has more of the forum open to guests than I have. I think it's just a case of getting the balance right.
A shout box or chat room may be useful. We use a chat room on both sites. The chat room does get used quite often and does prove to be popular with the members. It's not available to guests in a similar fashion to the arcade on here.
Having colour groups for differentiating between, admin, moderators, members, etc could be worth implementing too, again I have this on both the sites I look after.
Just a few ideas
