That's hard for me to say, since I haven't tried to do it both ways. Obviously if you have a long track record writing articles on the same subject, that makes a difference. At the point I'm at, I've got enough of that that it's not worth beating my head against the wall to make a few more magazine sales, they're clearly not going to make a difference. So it's not worth wasting my time on any more magazine pitches that people don't even have the courtesy to reply to with a rejection.
But if you're just starting out, does killing yourself to sell a handful of magazine articles help? I don't know. Previously published articles won't help if they don't love the idea and you haven't written a killer proposal and sample chapters. And if you've managed to write a killer proposal and sample chapters that shows everything that a magazine article could show about your abilities.
I think that writing for magazines has become so competitive that it only makes sense if your dream is to see your name on the cover of whatever. But it's not worth it as a means to some other end.