It's all about balance. If you only have a few forums but lots of posters, things are hard to keep track of because every second something is changed.
On the other hand, if you have lots of small forums, people have a hard time keeping track of the posts because they have to check every forum with new posts for a topic of interest.
HLP is in the middle; on average, I check 3-5 forums per visit which have fairly specific descriptions. I can quickly scroll down the list of campaigns and see if any progress has been made, since if something new comes up there'll probably be a new post or two.
The forums are fine as they are, and unless a new project is started or the community's population jumps dramatically, I don't see a need for more forums.