To add some ideas, I think if you pixel a non-repeating bottom with the rocks being different shapes, heights, depths, etc., and no two being even remotely alike just the width of the screen (but make the ends blend obviously), then when you move left or right you can simply loop it, and the same rock segment will never be seen. This also goes for the top. Also I the single line highlights are like a flashlight being turned on right in front of your eye, its just too bright in contrast to its surrounding colors, and it doesn't really fit. Also, I recommend you do this to the top rocks also, and not just vertically flip the bottom. It is like nature, no two things are the same, nor should they look that way.

Another thing. If the rocks on the bottom are rocks of "doom", does that mean the character does not walk on or touch it (without dying)? If that is not the case, I suggest you thin out the rock layer on the bottom, because then you have more room in the middle for the actual character.