personally, while not a typical piece in a tang tank, I would stick some sort of tall decor item in there... maybe some branchy driftwood? may not be the look you are going for though.
either way, what I think you should definitely add are some cyps... maybe even rainbows... get some fish that will occupy that mid-to upper water column! all of that said, it looks real nice, man. I have to find me some rocks like that!
-Rich