I think it's more what you put "inside" them rather than the outside and when the dog is healthy, then the coat is too, and will shine. Of course the cotton coats don't shine as much as the silky coat. I took this picture of Razael yesterday while they were all playing in their play room. This was not after a bath, but two weeks after one. She got a bath today.
The shampoo and conditioner I use on my girls is #1 All Systems. It's very concentrated and I can dilute it down as far as I want. Usually diluted down more in winter than in summer, but not by much. I buy them by the gallon and they last for my 4 girls for a couple years.