Polish .pl and .com IDN are essential if you own and have developed the ASCII counterpart. Other than preventing traffic bleed by pairing them up, I don't foresee any serious Polish developers ever using an IDN as a stand alone domain, they usually opt for the ASCII counterpart instead. I own and use IDN in this "support" format, and in this role they will always have a use in Poland.
Hypothetical Example:
bizuteria.pl [top tier developed and search indexed website]
biżuteria.pl [non indexed domain using forwarding or a redirect]
krakow.com [top tier developed and search indexed website]
kraków.com [non indexed domain using forwarding or a redirect]
There are three reasons why you won't see the IDN used as the main search indexed domain in this case, with the ASCII as the support domain. The first reason is that ASCII has been the top tier standard for so long in Poland, that everyone seems to be set in their ways on it. The second reason is that ranking an ASCII within Google is easier, and you will encounter less problems. The third reason is that Poland is so close geographically to countries that use other language scripts, that they always use ASCII as top tier because it has international accessibility, whereas the IDN domain is restricted to domestic use obviously.
My 2 cents on the Polish IDN angle. Obviously many Polish IDN have huge value, and pull down hundreds or thousands of type-in traffic visitors per day. That isn't going to change anytime soon, and so they will always have trade value and some aftermarket appeal.