Agreed on how the site was being run behind the scenes. The old vBulletin setup wasn't ideal but the migration attempts drove traffic away and the bass forum never really recovered.
As to how to increase participation, I'm not sure. You're at least hitting the front page of Google's search for bass guitar forums, though it's a bit lower on the list on that front page. Some SEO fixes may help bring in new users which is likely what the site needs. I think a number of us are holdovers from the older times that check in here and there but are still a bit reluctant to participate much. As for myself, I'm definitely in that group with the addition of not having been able to play bass much for the last couple years. It's no surprise my participation in bass related discussions on any site is pretty low.
Beyond that, I'm not sure what's being done to promote the bass forums within bass related magazines, etc. I do see some bass related info on the HC main page so there's definitely potential to get bass players to the site. I haven't specifically checked to see if those articles are also promoting the forums for added discussion or such but that might be a thought if not being done.