OK, I'm not a sensative guy or anything but I had this idea:
Why not add flowers to the terrain? Many flowers don't grow very high and are mostly just ground cover. So why not add them by simply painting them into the existing terrain tiles as dots or patches of primarily yellows, whites and blues with an occasional dash of red and apply them only to the open plains areas?
Similarly, downed and drying leaves, pine needles and even small twigs/branches could be added to the forested areas in shades of brown, rust and grey.
I think it would be a simple yet elegant addition to terrain immersion and would have little if any frame impact.