Thanks for all the input guys. I really appreciate all your thoughts and good ideas!

@Joker: I think the tutorial 'rising up the mountains' by Pasis comes really close to what I do. I use four layers for the mountains, 3 pattern layers and a normal layer on top.
The lowest layer is the hills layer.
Above that is a layer with the rough outline of the mountains
Above that one is a detail layer where I paint in all the ridges with a small brush.
And the top layer is a normal layer where I paint in the shadows and highlights with black and white.
Hope this helps.

When you follow Pasis tutorial, You will get very similar results, but if there is a demand for it I can try to make a tutorial.