I'd be tempted to put the tiniest amount of blur on your heightfield map, to try and avoid those verticle sides. The slightest slope will allow better texture cover. Also a higher bit per channel will avoid gradient banding, which will result in stepping in the blur.
As for your ground/rock textures, maybe greyscale them to use as displacement maps instead of colour, so that you then have full colour control in blending your surfaces with various slope dependencies.
Interesting composition.
