When I was working on a log cabin, I also worried that my lights and darks weren't different enough, but when all the blocks were assembled they were fine. I think your stars will also be fine when assembled. I also think that in a quilt that relies on lights and darks for a pattern it is good to have some areas that aren't quite as defined as others. It makes the eye wander around the quilt to assess the pattern. Your quilt is coming along very nicely. It must have taken a while to find all those polka dots.