As a previous RO player/GM (not counting my Admin time), I think the forum is somewhat helpful. You get to know a bit about the community (or at least one part of it). However, what frustrates me would probably be the Suggestions section. Sometimes, the staff doesn't even bother to reply or at least post reasons as to why the suggestion isn't as good. Kinds of leaves players hanging in the dark.
I do agree though most players don't have forum accounts. That is kind of sad to me because they should be active on both the server and forum, but I guess they prefer to type in-game. In fact, they type too much in-game for those who don't have forum accounts (complaints and such).
I still believe forums are necessary to each server. Maintenance calls, updates, guides, recruitment for guilds, and others are pretty good sections for players to see. Forums are not completely useless in my mind.