The easiest way to add some detail to your terrain is to use a detailmap.
Just create a small (f.e. 128*128) tileable greyscale texture and add it as the second skin to the hmp file.
This page is in german but on top are two examples for detailmaps:
http://www.darkmountain.de/detailmap.htm
It will already look much better, though a multitextureshader would be even cooler