It was up and down when I first started, but the more hubs I made, the more I seemed to get. I think when you reach about 70-100 hubs you get a massive traffic spurt. I have confirmed it with a few hubbers in the forums and also a friend on Etsy reported the same thing when she had 100 items in her shop. So if you accept the benchmark to get good traffic is 100 hubs, then you'll understand the kind of persistence needed to earn more than a hamburger a month!
PS - You also get better at promotion or SEO too, the more you publish. This also helps push it up.