I hear a lot of people recommending hitting every zine you can with every article you write. Some claim that's better. I say it's hogwash. If you know your subject well, it's not at all difficult to write several variations on the theme. The investment of time is worth the effort.
Nothing is more valuable than that for a writer except their own established readership base.
You get more credibility and actual readers from an established and well run publication with 100,000 subscribers than from 30 mediocre ones with 5,000 subscribers each. A LOT more, even ignoring the issue of subscriber overlap. You do better work when you know it's going to be read by a lot of people. That quality of content is important for things beyond the original distribution. There's more mileage in it there than in any publication.