I'd suggest that you reduce the number of categories to a much more manageable number, like two. Right now there are so many categories that any given question could be posted in three or four or more areas. The poster might miss the person who could answer their question or the poster may post in all categories that he or she thinks might apply.
Go to Cartalk,com and look at their bulletin board. It had only two categories, one to discuss the show and one for car questions. There are no sub categories for type, make, area of question or any of that. Everyone jumps in the same pool, and this is a very active board. I think this board would be a lot better if it was done the same way.