The only things I can think of to change the repetition a bit is indeed a warp effect, but not only by fractal warp, but also a warper and vector displacement + PF, where you have more control. Perhaps also a second set of the image map, with a transform shader attached to rotate it (or move), then merge using highest raise, see if that gives a nice result (theory), you'll have less valleys, but it might turn out interesting.
Regarding getting the slopes straighter; add a compute normal after the initial up displacement, and add a distribution shader with a soft minimum height at valley bottom (plus perhaps a masking PF for randomness), and pull through a displacement shader set to lateral. That should displace the higher altitudes along the newly computed normal to the sides, i.e. into the valley.
