Okay, I like a number of blogs I've read on WordPress. However, in attempting to reach specific audiences, the concept of Categories or Tags only takes you so far.
The primary problem is that the categories and tags change whenever a blog is posted. Something more static and stable would be a great boon for WordPress overall.
I believe that an additional field should be created
(1) to better describe the author and the purpose of the blog, almost categorically- NOT like the about me section, but a searchable aspect which anyone can use to define their blog; a meta-filter category of sorts, which might be searchable based on characteristics such as age, education, profession, whatever...
-Because I prefer the anonymity of a blog, however, I also suggest that you (2) include an additional sort of a meta-category for intended audiences:
Again, the characteristics could be broken into categories such as age, ethnicity, genders, etc., but could also include primary purposes for the blogs.
The point of this is to have an optional static purpose/intent for blogs' authors and their intended audiences. It provides a supplement to tag-surfing as well, which is a nice benefit.