I took some of the rock out as it started to look bad for the sponges and have probably only half the rock left. But like you and Brian, I have tunicates and sponges growing like crazy on the undersides of what's left now. Most of the coral that came on the rock are still there too. Not sure how that happened!
I'm actually considering getting some more rock and curing it in some tubs for now and adding it to the tank to fill in the gaps.
What really bothers me is the fish I lost. I had a beautiful ( to me atleast ) Tomini Tang and Scribbled Rabbitfish that were buddies. They both died as well as my little group of Anthias.