Well I heard that the velvet damsel will loose the nice accent stripes as it matures. That is what I love about that fish. She (Grettle, maybe a she) has been picking on things already, especially the feather dusters.I think the only way you will be able to have anything else in that tank, especially a clownfish, is if you get rid of that velvet damsel. He will get big and mean very fast and terrorize everything in the tank. I even added mine last to the tank and the damsel still was mean to the other fish. In a 30 gallon, the damsel is going to outgrow really soon and he'll probably beat up the blue damsel too.
The yellow tail damsel (Hansel) is the most awesome blue, I really want to keep that one. Then maybe some other bright colored fish, maybe a blenny.
Who knows, I am not adding more critters for awhile, but maybe some more macro algea or rock.