Considering how many Polarii there are, and the typical failure mode, I'm surprised that someone like ChipForBrains/Technology Transplant hasn't bothered to make a replacement overlay. They made a small panel for the Prophet-600 and the Moog Source (if memory serves), and there are oodles of companies out there who could make the panel:
I'm sure it wouldn't be that cheap for low volume - but I think if mine finally breaks for good, I might consider it. A Polaris with a self-illuminated panel (http://www.lumitex.com/membrane_switches.html) would be pretty unique.