I currently do not run any forums, however I have done so in the past for a hobby and not money.
I do think that running a forum for money requires a balance of passion for communities (specially the one your are running) and sense of making money. It needs to be moderated correctly and choosing moderators has to be tactful and trustworthy to ensure the rules are applied, and constructive feedback is provided as a team.
When I did my hobby forum, I slowly added Google ads in order to cover the forum and domain costs and eventually surpassed it to a few hundred a month without even trying. The focus was within the community ensuring it was as smooth as possible and not making the money. I think if my focus was on the cash (which is great

of course) the community wouldn't of gotten the attention it deserved and died off. Since i wasn't looking for $, all the funds went right back to it's community for prices, perks for top performers, copies of software/games, etc...
I personally think having it strong and consistent community, makes it's value stronger (looking at the business side).