We've resisted subdivisions before for the simple reason that we don't want to encourage or discourage certain topics and would find it difficult to choose subforums.
For example, we're not a sports-themed site, so it doesn't seem important to have a specific subforum for sports, but you are right that we do have a number of sports threads because many people are interested in sports. Even if the case for a sports subforum was clear-cut, there are so many potential subject areas that it would be quite difficult to decide on the categories. I bet we could name dozens of potential categories without much effort.
We do try to keep Apple and Mac and other computer threads out of Community Discussion, for example, moving threads about PC games to the Games forum, questions about shopping for non-computer ideas to the Buying Tips, Advice and Discussion forum, threads about current events to Current Events, threads about web sites to the Apple, Industry and Internet Discussion forum, and so on. What's left is supposed to be a catch-all for all other topics, i.e., what you call "Special Interests".
As often happens with Forum Feedback threads, I've jumped in with an explanation of past policies, but without an intent to cut off discussion. We really are open to suggestions like this. Please share your ideas about it and tell us specifically what you would find most useful.