I liked your start and thought the second iteration (rock stone 3.jpg) showed some nice improvements.
This latest update makes me speechless, I just don't know what to say, but only ask uncomfortably: what did you do to your nice render?
Please revert to your previous version and make small step by step/incremental changes to your scene.
Indeed, to brighten up shadows off your terrain/surfaces you can do 2 things in your situation:
1) decrease cloud density to allow more light pass through
2) increase "strenght on surfaces" setting in the "enviro light" node. Say from 1 to 1.5 or from 1 to 2.
Good luck and take it easy with changing stuff!

Cheers,
Martin