Those bushes look rather usefull, in some good renders.
I had a dabble with trying to smooth out terrain along a paint shader mask, firstly with blues, gave up, and went with heightfields and the "heightfield smooth" function. Your landscape is generated in the normal way with power fractals, but you then convert them into heightfields, one vanilla, the other smoothed, then combine them back again. As in the node set up.
I'd be tempted to take a top down render of your painted mask to add detail in a paint program, to get tracks to follow the curve, then bring it back in to apply colour and displacment.
Anyway, an interesting little exercise which maybe usefull for someone.
Cheers
Jon