Well, until I see some testing proof, other than anecdotal evidence, I'm not convinced that turning an incandescent bulb on and off frequently, significantly affects its life. I believe the filament heats up evenly (albeit rapidly) when the bulb is turned on without overshooting it's normal temperature, thus having no significant effect on its lifetime. I've had bulbs in refrigerators that have lasted for many years (I don't ever remember having to replace one).
The hot/cold resistance ratio has nothing to do with the bulbs operating voltage. It's caused by the hot/cold difference in resistance of the tungsten, which is determine by the bulb operating temperature. If the 12V bulb has the same operating temperature as the 240V bulb, then its hot/cold ratio will be the same. Similarly the peak power is the same, since the inititial resistance of a 12V bulb is proportionally lower than the 240V bulb.