It sounds like the biggest 2 concerns with creating more sub-forums are these:
1) Topics may be posted in the wrong board (either intentionally, or because a poster didn't know what their solution would require)
2) The volunteer admins would have more work trying to move things to the correct boards.
I wonder though if the added organization would be more friendly to the average user -- not just the long-timers/volunteers looking to answer posts that haven't had a reply yet. What happens when you do get a reply, but need further follow up. Your post can't be found as easily anymore?
And, I'm not sure what real harm is done when admins don't have time to move (or don't notice) a misplaced post. If it stays small, then no big deal, right. If it gets large and is eating up space on page 1 of the board, then it's noticeable, and will get moved. And yes, maybe someone will search a sub-forum and not find a relevent post that was posted to the wrong forum, and so would post a duplicate question. Still, no harm there either IMO, since duplicate posts already happen, and it's not like we're writing gospel here that must be archived in it's untainted original perfection -- the responses to the second may contain a new solution not previously mentioned.
Just some thoughts. If people like the current setup though, that's how it should be.