Personally I do not think any more detail needs to be added to the head textures , simplicity can be a good thing , something that this community lacks when it comes to textures. Everyone thinks in order to have a good texture they have to detail the crap out of it , this is not true . The painting world is a good example.
I say leave them as they are , the textures look great. Stay with that style for the rest of the set too and don't let anyone change that.