On a more serious note, we seem to forget one thing. The car was originally engineered to have too much brake force at the front and too little at the back, to avoid customers locking the rears. If you remove the proportioning valve, you don't remedy that, on the contrary, you push even more of the braking power to the front. Now even your wife can drive it on ice...
Anybody with an original setup should either do the whole thing, or get better calipers for the rear. If those calipers are good enough to significantly increase rear brake force, then it might make sense to remove the (dare I say it?) proportioning valve.
This winter I'm removing all my orig brakes and installing kit from Dennis Quella. My expectations are high...