You might notice I'm making extensive use of layer masks. I find, in short, that they offer a non-destructive way simply to paint and erase terrain features. With cunning use of layer effects, you don't even need a layer fill itself. In fact, most of my layers are just white pixels; everything is applied via effects and alphamask densities.
I also find that it's quite easy to DISTRESS a layer mask with various filters and procedures to achieve results that you can't get by using similar procedures and filters on the painted layer itself.