BTW this thread has convinced me not to let CAGI drag enemies through obviously damaging spell effects, should that ever come up! It's pretty unlikely but a theoretical corner case.
I wouldn't worry about it too much. There are combos which are far more potent than CaGI and a damaging effect.
One which comes to mind is one I was party to. In a past 4E campaign, both my character and the character of another player had access to Thunderwave. He was a wizard, and I was a half-elf; I had gotten to a level where I was able to turn my Dilettante power into an at-will. A potent tactic of ours was to put up a damaging wall between us and then proceed to play Thunderwave ping pong.