It is not really about roads and rivers , but...
Here I try to show where IMO the problem of Falcon 4 terrain rendering is and perhaps we could counter that with new way of distributing patches of variable terrain over the homogeneous nature.
Below an example of the desert terrain with "variables" introduced into the mix. I believe that there are around 8 variable textures here , but this does not prevent them from being unnaturally repeated (sometimes in immediate neighborhood). Also what is noticeable is the impression of grid.

From higher altitude that is even more pronounced and downright ugly
It is progress shot and the river tiles for that type have not been yet found , but the shore is made and in more than one variation. Notice some tiling anomaly caused as I believe by the river proximity to the shore.
Going back to point of this post ......
Instead of variable tiles my suggestion is to counter this with small patches of another type of the terrain which can be introduced as a some noise in CATE background template. This would be no more than few pixels/tiles per patch, and only in the areas free from roads and rivers. Desirable, there should be quite few types of such patches over homogeneus terrain , but all should be rather not too far as far as look and color are concerned.
I envision that the effect of such a patchwork will add a lot of realism to terrain and can be looking something like this:
IMO variations to terrain various in size (larger than a single tile) as well as texture and content will give as desired results.