I hope I'm not too late to give my 2 cents.
From my experience, "shareholders" (admins + mods) are still playing most of the role in developing forum until the forum is mature. Before the forum reaching the desired quality, of course, we can't expect users to generate quality contents that will affect SEO and stuff for free. Just give incentive to good posters to take part in the forum with a position, and later when there's revenue from ads etc., it can be shared with all "shareholders." The revenue can be shared with "stakeholders" (all users) as well via internal signature campaign to generate more quality posts. Crappy bounty will only attract spammer and it's not good.