I don't drive (I don't even have a drivers liscence). I am of two minds about what you are suggesting - but basically my opinion is that if you have a car, have a seat - JIC. If it is a JIC seat, then a cheap second hand one should do, I mean if you plan on never using it, it hasn't cost you much, but if an emergency arises then you have it. If you are getting rid of your car though, then you obviously don't need one (but I have found having a spare one handy is a good idea, if only for when others babysit, etc).

Also, hire is a good option - But not in the middle of the night, plus you usually have to drive to pick up the seat in the first place. And relying on others generousity is not the best option either. I personally would never lend my kids car seats out to a friend, and would feel arkward and put on the spot, if they ever asked.