Finding myself spending enough time on everywhere else on FT, I personally spend very little time on OMNI (perhaps a few hours a year).
However, I think it provides a vital service to the rest of the boards. It allows the community a place to hang out and chat among friends. It provides a place for discussions that folks want to have but don't fit into the other well defined arenas. It reduces the tendencies for threads to go off-topic due to pent up demand to discuss certain issues (whatever they may be). Without OMNI, instead of directing someone to take an off topic disscussion to OMNI, we would have to say instead "Shut up, or go elsewhere." Not a very friendly message.
I further believe that the existing system of controls on OMNI do a good job of managing it's growth: keeping participants to the FT community (those interested in points, miles, and travel in general) and reducing the number of trolls.