Thank you Cliff. I've gone back and forth on whether I should add more rock or not. I finally decided not to for a few reasons.
First, having less rock gives my fish more room to swim around. In a similar vein less rock provides more water volume. This gives me a little bigger margin of error as far as water quality goes. My 29 gallon tank probably has more water in it than some 35 - 55 gallon tanks.
Also, having less rock means less corals to put on it, which saves me money. I'm not even tempted to buy more corals any more, because I don' t have any room. In fact I've already given some away.
Lastly, now that the coralline has taken off it looks more natural than before. So I'm pretty happy with the looks. I hope that eventually the whole back glass will be covered with coralline algae. Which I hope will give kind of the effect of being filled with rocks.