Agreed, I like this too. You can't really tell how big the rocks are, but maybe that's not important. You could always try adding some shrub or grasses in the lee of some rocks (just use the big rocks (perhaps whitened using a color adjust shader) as mask and shift to one side using transform shader, then subtract original lightened rock mask, test on ground and apply as mask for grasses).
I have to take this back, as just testing my never tested theory showed it doesn't really work. Which I don't understand....