I think you should begin developing a "website member management" program. It should integrate with all the programs you currently have along with web boards.
I would like to see several levels of memberships. When a paid member the member should display a small logo of sorts beside his/her name. Like many programs it should automatically warn of pending termination and give them the option for renewal. It should allow the control of access to specified directories.
Your current programs could have special integration for paying members, like more webspace or special pricing on ads.
What do you think?