Here is another proposal that I hope you'd be interested in:
Select a few individuals, three or less probably, to actively moderate the forums.
The reason for this would be to add some metadata and a little bit more order to a forum that is still rather manageable with only hovering around a thousand topics. Possible tasks could (and in my opinion should) include:
* Look through threads, if it's a problem that's solved, modify the topic to say so. For example "Rendering broken" becomes "[Solved] Rendering broken"
* If a thread is clearly more an open bug report than a discussion, add it to Mantis, add additional information and lock the forum topic after addding a link back to Mantis.
* Move all old bug reports to Mantis so that this subforum can be deleted without loosing information.
As you can see, I'm merely advocating extracting more information from the forum posts rather than policing the users. I'd certainly be willing to step up to the plate and do some moderating but I'm a bit skeptical if I'll have the necessary background knowledge to successfully improve upon existing forum bug reports, for instance.