Haven't tried Nioxin, but isn't exfoliation more for addressing dandruff issues, not thin hair? In case you're interested, here are a few suggestions that have helped me with thinning hair. I'm especially happy that the parts around my temples have grown back in, since they were looking really sparse for a while...
1. Have you had your thyroid checked lately? The instructions for labwork as given on stopthethyroidmadness.org are especially useful, even if you have previously been told there is no problem w/your thyroid (my hair began thinning due to previously undiagnosed thyroid disease and later when the Rxs weren't working properly).
2. Consider taking a Biotin (b-vit) supplement (or a Hair Growth vitamin and mineral formula to make sure you have your nutritional bases covered). If you read the reviews on Biotin at a place like Iherb or Vitacost, you'll see lots of people with thinning hair raving about it, too.
3. Brushing at least 100 strokes kind of hard with a Mason Pearson (or similar style) hairbrush daily (really gets bloodflow (nutrients) to the scalp to stimulate your hair follicles for growth).
Those three things have made a big difference for me. My hair is still dry, but it's a lot thicker than it was...