When I loom over some of my old images taken with my unmodded 300d, and then my modded 350d its chalk and cheese. Although the modding is to increase the H alpha red light sensitivity, it seems to let more light in of all colours, as the standard canon IR cut filter has a very gently slope and seems to block small amounts of light further towards the blue end too. My modded 350d is even more sensitive than my newer unmodded 450D that I use for daylight photography now.
Scott