I live in MN and because of the bad winters, our roads are quite rough.

Kind of weird question, but..

Sometimes i drive the car and feel like I am doing some damage because its just such a bumpy ride over all the rough roads.

I realize its hard to give me a definite answer -- its probably certainly causing some wear on the car..

But how bad is it?

Are they pretty durable with this stuff?

 

I can't speak for a 911 but my cayenne needed frequent alignment on rough roads of New Orleans. I'd rotate the tires and have them re-aligned when I noticed uneven wear about annually.

 

But they weren't way out of alignment, and it wouldn't prevent me from buying another.
Also in other non-porsche cars and SUVs I either never aligned them, or I'd only align them when getting new tires.

 

Your roads are no worse than mine. The 991 holds up extremely well! No extra alignments needed. No extra tire wear. No worries.