I think it would all depend on what the DLC was and what you thoght of the game to begin with...
Personally, for games like FO:NV, I am waitintg to buy the DLC until after i can get a cheaper bundle for them.
With multiplayer modes, there could really be DLC coming out for RAGE for years to come.
I will most likely wait for at least a bit with RAGE DLC, unless its something pretty snazzy.