I would not worry if it's short term fluctuations, weekends and holidays affect visits and comments, usually getting quiet around the weekends and picking back up by Tuesday. Also, I have noticed greater rises and drops around holidays as some people are more inspired on the days preceding major holidays.
You also have to figure in that after major holiday seasons like Christmas and New years, there should be less traffic in January. January and February are the low traffic times for many physical businesses like plumbing or retail stores, and I expect the numbers online to reflect that somewhat.
I don't watch my traffic very closely at all at this point, but I do notice that my income remains steady so far, I am always earning a little more every month now, and this month seems to be on the same track as the last 6 months as far as increase, so I'm not really sure how that is all working. I haven't even written a hub for a long time! However, I do visit the questions section quite frequently and I make an effort to comment on other's hubs so that is likely a factor.
I think it also depends on what kind of traffic you are getting. Like for you, you are probably looking for more Google traffic and your hubs are focused more on marketing, which could be why your traffic is fluctuating more. And I'm not saying that's a bad thing at all, but that you may have to approach your Hubpages efforts a little differently than others.
Also it takes time to become established. I did not start out to become established per se, but I think longevity along with writing quality hubs and writing often help alot too. I think many of my hubs could be considered quality, but I haven't written as many as others have and if I did, I would no doubt see a huge jump in my traffic and hopefully income.
It seems there is a formula, but part of it is something incalculable. Probably putting out information that people are seeking and writing with those people in mind will help alot. I don't know how it goes exactly, but it is as someone said, 1% inspiration and 99% perspiration. Keep going and see what happens in a year.