Steve Yelvington has posted an absolute must-read entry on his blog, where he breaks down the two major types of visitors and the ways you should serve them:
The beat blog focuses on the small circle, offering speed, depth and conversation among the reporter and people with high interest in the subject matter. While regular users are the primary beneficiaries, there is a secondary benefit to the casual user: the reporter gets better at his or her job. Better leads, better feedback, better ideas can lead to more interesting journalism.
And then there’s the topic page, which is what your less engaged, occasional visitor wants. Go read.