Making details that aren't cartoony is more a matter of lighting and hilights. Having some good repeatable base patterns to mix up the solid under colors is a good idea aswell.
Here's a quick hatch piece I made to illustrate. It uses nothing but the basic effects available in photoshop 7 along with the shape tool to make circles and lines and the gradient tool to help mimic shading/highlights in certain areas.
Its not the prettiest hatch, but I think it would be alright to use on a tiny little tank like those in generals.
In the very least it might give you some ideas for yours, I don't know.