Simple adjustment or time for a new machine?

My thread tension is driving me crazy! It seems to fall in and out of proper thread tension randomly. The picture is of the underside of a piece of fabric - I'm not convinced that the upper thread tension dial actually does anything, so my questions are as follows:

1. I've tried sewing with upper thread tension set everywhere from 0 -9, checked my lower thread tension, rethreaded the machine - is there something I'm missing?

2. If this needs some sort of repair, I am just going to bite the bullet and get myself a real machine, any suggestions? I've been looking at the Singer Heavy Duty line, but a few of the computerized models seem to have a lot of good reviews on the internet (I have a Sunbeam right now, I don't love it, I mostly do small quilting and clothing projects - definitely beginner-Intermediate level...)