It was always my understanding that the plastic screws that were used was to allow the screw(s) to break, and not what they were attached to. IE: KZ1000P has about a dozen or so plastic screws holding the Plexiglas windshield to the fiberglass fairing. Don't ask how I know, but when you go off the bike backward and hit the Plexiglas, the screws snap off. This prevents damage to the fairing and/or the rider.
The screws are cheap and easy to replace.
Steel hardware will not give. Either the winglet will give or the fairing will. Neither of which are as cheap as plastic fasteners.
I don't have the winglets since I want as much airflow as possible when our temps get over 100°.