It has great potential, this image. The lighting is very dramatic. I partly agree with Martin. If I had this file, I'd get (as you say) a little more wisps in the cloud layer (blending it by small stretched ridges), but not diminish it, raise the POV 20cm or so, so that less of the dark foreground is visible. But I'd keep it quite dark to keep the drama.
The stones may need to be rounder, and you might as well do them procedurally, with some hard billowy fractals for lichens.