I personally like forums, although I don't post all that much. I find it's a much better way to post and find specific things when you need them. Besides, the forum seems to be a lot busier than the Facebook group lately.
Couple ideas to keep things flowing is to maybe have dedicated moderators for specific sections. For example, have people that do a lot of autocross/track/strip events run it and keep people up to date on events that are coming up. We've got some good BSers on here. Maybe have them run the off-topic section?
On bringing people back, maybe send out an email to those who used to be active, but have fallen off, to invite them back. Might drum up some more log-ins.
Slow day at work. Figured I could use some of my skills from there and transpose them to here since they're being wasted anyway.