Sean, the problem I see with using grains is that color film (if I'm remembering correctly) uses dye clouds. This is why the C-41 B&W appears so smooth (and less sharp--look to the paper sharpness thread or Barry Thornton's Elements of Darkness for this one) compared to traditional B&W.

I really like that suggestion though! Just want to set-up the counter-argument, but I think it doesn't warrant enough merit to knock grain out of the running.