Like in my post about outposts having special abilities, I think the same should be for Vehicles too.
There is the Utility truck with the snow plow blade on it, I think having such a attachment on it should mean that zeds cant jump on the hood and smash the engine, also that upgrading the truck would improve on the blade, adding even more armor to the front.
In SOD1 there was the little piggy tow truck, being able to use the tow truck to actually tow vehicles back to base or other locations like outposts would be a great thing, most of all for solo play.
The Ambulance could generate a single med pack, if there is space, every day but wont if there is already one inside it. It should also keep some general semblance to a ambulance when upgraded too.
There is also a truck when upgraded looks to have fuel tanks on the back of it, I think that it could be used to siphon gas OUT of a vehicle, maybe one you dont want or need, maybe even out of the wrecked vehicles on the map too.