I think as it stands BB has three problems:
1) motivating new teams to stay in the very first weeks
I believe this might be the most important task at hand (allthough you probably have statistics on this). You need to keep people busy long enough to get them addicted.
Easier access to forums is mentioned, but I belive alot could be done to make the game more active in general.
As mentioned initially you have an active community, and the forums are buzzing. So, obviously alot of people have alot to say about the game. However, the game does not take advantage of this (other than in the forums). IMO you should make more visible what's going on. How about a "News from around the league" with news bulletins, transfers, news from the national teams, game results and so on. Alot of the information allready exists, and you could maybe add small stuff like "player/team of the week/month" (with a small price), milestones (NN just played his 100th game for TEAM X), and so on.. The possibilities are endless, easy to create (I would guess), and it would add to the fun of logging into the game on an every day basis.
I also like the idea of people acting as mentors. I don't think it would need to be anything advanced. Perhaps a sticky in the help forums where mentors and new teams could "hook up"?
And of course, a tutorial for new users. Perhaps "unlocking" secrets of the game (hints, tips) the first few important weeks, would be useful to keep people busy.