I don't dissecting large texts piece by piece. I feel that it... I dunno, de-legitimizes it somehow. Makes the advice seem less helpful then it actually was. So I'll reply as-is.
You're damn right about my total values being weaker then they really ought to be; somehow I think this stems from my actual creation process, what with the amount of black lines I use throwing my original value estimates off and screwing up my darker colours in particular.
The troubles with this particular piece's values, though, originate from the fact that I hadn't decided on the actual specifics of the light source until after I had already done the rocks... and as your paint-over pointed out, that was a mistake.
So anyway, thanks for the tips, and I actually tried to apply some of them here. Went for a much looser sketch, so that I'd be able to get my colours right without a bunch of pesky lines interfering. Also tried to block upwards in value instead of a middle of the range start. I think it worked out alright, even if this is technically a relapse into fanart.
Went for a nightlight effect, and didn't do anything with that motherfucking background.