You'll get a plastic card, which is more than enough to identify yourself with to the government
As for the plastic card, my current passport or driving license seems to suffice whenever I need to identify myself. Nobody asks any questions.
Someone else might see it differently, though, especially if you were married the entire time.
I will simply have to enquire. My friend will be able to inform me as he has already completed this process. But, yes, I was married the whole time and event prior to this period in Poland so it may count for something.
In all honesty whenever I do need something from the local Urząd they normally don't cause too much of a fuss. That normally boils down to the fact that they themselves aren't entirely all sure about the process, or they never used to be. Although, Poland is progressing now and they are more on the ball about these things so who knows! Thank you anyway.
It's not an urgent necessity to have citizenship. I would, however, like to complete the permanent residence procedure prior to Brexit and hopefully prevent opening a can of worms.