It all depends if you are trying to model a specific region. I attached an image of an Appalachian Mountain Cliff. Similar to yours, but with some buff and reddish hue's.
But honestly, to my eye GREAT! I like the strong contrast, highlights & shadows. Very pleasing to look at. Looks like you're testing the waters, experimenting is the only way to achieve the desired effect that's pleasing to you. I'd be extremely happy with that formula and would be interested in your process to achieve your effect.
Forum member "JOHNF" just replied to a post 10 minutes ago, "topic/plaster-rocks-and-acrylic-paint?" see link:
https://ogrforum.ogaugerr.com/...35#77311805230446135