Ok I have added a forest texture with an open grassland texture around it.
At this scale it's not easy to find a texture that will give the impression of forest or grass without messing up the visual scale.
I like the mountainrange a lot. It looks very natural. With 'trailing remnants' I assume you mean how the mountains recede to hills? Like the small ridges around the actual mountains? I think those look very good, though you could make them blend a little bit more with the background.
Can't really help on the textures. Right now the forests and the grasslands seem very alike in texture, perhaps making the grasslands smoother (through lowering the opacity or changing layer attributes, I think simply blurring or smudging will end up looking not that good) will make them look less similar.
Yes the trailing foothills do seem to stand out a bit much. Lower the opacity a little and let some of the forest come through.