Posted By:
JoannOK - I'm going to be a little careful here, since I've only recently found a voice and stopped lurking.
If there are boards for other topics that aren't active, then it suggests that there is not enough interest to sustain them. If the desire is to attach those topics to this board because this is where the people are, then it may dilute the value of this board by creating clutter/noise/extra navigating for what may be marginal topics. (Again, going with no knowledge, and strictly by the comment that the other boards aren't active, I'm inferring that maybe the topic is marginal.)
I often see - in life/work, etc - that once something starts working well, people want to hitchhike on it to accomplish other things. If a manufacturing order ticket is the only thing that is known to reliably make it's way into the hands of a production foreman, then people want to start adding all kinds of things onto the ticket - special instructions, inspections, notes about shipping, etc. So the things ends up being far less effective at what it started out to be because people used its reliability, its effectiveness, to try to do other things.
That analogy may be a little off, but if there is desire to include posts on other topics, none as universally desired as the core topic, and none quite able to sustain an independent forum, then to me it would cause the effectiveness of the whole thing to deteriorate.
I'm avoiding stating an outright opinion on more vs less topics, although I do have one. I'm only pointing out that if this board is used to help prop up less broadly popular topics, it may damage this board.
OK. Fire away. 
Joann