Just to inspire some thoughts:
In the radio control truck/car world all manufactures use "standard" plastics.
Often these plastic parts such as suspension arms, bearing blocks, etc. will break easily and often.
It is known by many to upgrade these parts made by an aftermarket company called RPM.
http://www.rpmrcproducts.com/
This company guarantees their products from breakage and are made of a Nylon material.
I've never broken one of their parts, but many OEM parts made from "standard" plastics.
I'm not saying you should change the plastic, but I'm just offering some experience I have with RC's.
They survive the impacts because of the flexible nature of the Nylon.
With that said I do not know how positively or negatively that may have an impact.
I also like the idea of inserting a bushing into the pulley until a more permanent fix is determined.
We will probably source something tonight as a bushing would at least allow the pulley to remain fully supported on the axle if a failure were to occur at the bearing.