There is another consideration for using higher voltage, ( as in CMOS at 12v that I designed around for 40 years until I saw the Arduino light )
With 12v CMOS logic there is a typical 0.45vcc noise immunity , so 4 volts of noise on an input can be tolerated without it corrupting an input.
I havn't yet built an embedded Arduino project for a car ( although I do have one in the pipeline ) but I would be wary about using 3v3 logic without a buffer and filter for that notoriously ( electrical ) environment.