i would be inclined to have a seat, even if its never used.

i love using PT when i can, i only drive when i need to do the weekly grocery shop. ut i would worry about the JIC moments too much. an example for me would be back in march when i had a miscarriage, i woke @ 4am and dp drove me straight to the hospital.. we had to do 4 more trips to the hosp over that weekend, and without a car seat, i would have had to either call an ambulance(and go on my own i guess) or not go at all!

i say better to have one and not use it, then not have one, and have to figure out how your going to get somewhere in a major hurry without a seat!