i dunno.  i've found the better my render is to begin with, the better it is after post.  or rather, the closer it is to what i want.  i spend a lot of time painting hair, but it's always better if i have a good base hair to begin with.  as a result i've spent a lot of time on my hair shader.  and the only GC correction i can find in Photoshop isn't as good as just using GC materials, but maybe i don't know the right place to look. 

basically, that's not what i've found.  i'm not saying that i know enough to be definitive, but i've definitely found doing as much as i can in the render to give me results i like better.  even for more illustrated looks.