I would like to point something out about the fire trucks taking so long to total.
I believe that if you drive them into a gas pump at a gas station, it will instantly total the truck, even when it's driving really slowly as it does when it gets too beat up.
I can't help with the respawn times but that does seem to be a quick method for totaling them if you can find a gas station which is not hard to do.
EDIT: It appears that this method is risky as I just died trying to do this a second time.
Last edited by Alpha X; 05-22-2011 at 04:52 AM.