I darkened the image a bit
I have changed the Levels (ctrl+L in photoshop)
I have also created a new layer, cut around the track, and used the render clouds effect, then set the layer filter to multiply, and opacity to 64%
And i also found a sky image (texture) from
http://www.mayang.com/textures/ and set that to Overlay, 100% opacity, it sort of adds some shadows and parts where the sun is shining through, just stops it looking plain.
Best thing is to just mess around, and eventually you'll find something that works