The wpf should only give a very minor (say, up to 15-20%) discount even if you stack it up to 200 wpf. The main effect is to INCREASE the maintenance costs of weapons for which you have low wpf. Not by much, 50% at wpf=1 and 0% at wpf=100 is enough. It is mostly to discourage carrying expensive weapons with very low wpf. DISCOURAGE, not prevent in any way.
Yes, side-xbow and throwing hybrids, I am looking at you!