Seat belts have to be one of the cheapest things you can do to avoid dying prematurely. A ruffled suit and a little less range of motion is definitely worth decreasing your risk of death.
Doing a Google search, I found some statistics from NHSTA about seat-belt use. About 75% of Americans wear their seat belts regularly but those who do not wear them account for 60% of all traffic fatalities.
Seventy-three percent of the people who were involved in a fatal crash in 2001 and were restrained survived; of those who were not restrained, only 44 percent survived.
I am happy to take risks, sometimes riskier things than going without a seat belt, but this one doesn't seem worth it.
But hey, I understand that people who were not brought up to wear them have a hard time changing. So many times I have had to remind my 60 year old father to buckle-up when driving with him and it still hasn't stuck. And he's been in a bad car accident before.