I would plant one end, then scatter a couple small rocks in the middle leading to a large rock pile on the other end.
I like it. A long twiggy piece of driftwood is a good suggestion, hard to find one that's 'just right' though...at least that's been my experience.
I think it looks pretty good as it is. But maybe a long thin or twiggy pieve of drift wood along the length of your tank. Or some tall stem based live plants.
