I ordered the KYB "strut mounts" once a long time ago. They were nothing more than the rubber donuts that you put in the actual spring perches to stabilize the shock piston. Yeah, they are not much different than the OEM rubber ones and I returned them.

About switching them to polyurethane, I honestly don't think you'd feel much of a difference at all. If you can do so cheaply, go for it, but I wouldn't expect much.