Interesting. Should a diffuse texture always be high contrast? I created a texture that to my eye looked great. But after tweaking with the histogram the texture was very low contrast.
I would say no. It really depends what you are painting. Example: If you are painting wood. Wood is usually fairly monotone. Metal is another that you want very little contrast in. More contrast in the spec than in the diffuse. There is never usually a set "rule" for everything. They are just tools... And not every tool…