Okay, so today I've been tweaking the granite mountains. I wanted to to create the appearance that the areas outlined in white were higher than the surrounding granite peaks.
And this is what I came up with.
Compare with before the change.
Basically, I duplicated what I did with the hills layer - I created the height map and did a few bump map layers based on that, but didn't add a color layer. The effect is subtle, but I think it does what I wanted it to do - creates the illusion that those areas are a bit higher than the rest of the mountains.