> But heck, even a parking light will flatten the battery if left overnight.

Nominal modern car batteries are about 12.6 volts. I wonder if the high-resistance bulbs will completely dim once the voltage drops to a specific threshold, say around 12.0 volts. If they do, then they should leave just enough charge to crank, as most starter motors can safely crank over with about eleven and a half volts (and all the way up to over 14 volts).

That might be an interesting experiment to test.