I believe, and I am not sure about this but I am pretty sure, that Nioxin shampoos are designed to be 'mild' on the scalp, but at the same time they pack Saw Palmetto.
I don't believe that Saw Palmetto is a substance that is readibly absorbed via the scalp and into the skin in enough quantities to do any difference. So, I think Nioxin shampoos are similar in effect to using Progaine shampoos. They are mild and non-irritating, but not proven by any serious study to have any actual benefit to your hair.
If you are going to spend money like that on shampoo, then spend it on your antifungals, such as Nizoral or T-Gel. If you want a mild shampoo, try Paul Mitchell Shampoo 1, which is a quality mild shampoo, as mild or more mild than Nioxin, but at much less cost.