1. Vehicle poses
I think that driving a vehicle should allow you to do a special kind of pose using said vehicle, viewable by people outside. For example, %V revs it's engines, or %V pulls up next to the Orifice. It's already been pointed out that some people would use this to do stupid shit like using their vehicle to "ram" others, but how is that any different than someone using poses to punch someone in the face? (As an extension of that, minor gripe. Before I brought this up, I had an NPC 'punch' my windshield. I found it very unfair that there was no way for me to retaliate other than either ignoring him or flying away. In-character, there were a lot of things I could have done, like nudging him away with the vehicle or moving just out of reach. I would've liked the opportunity to respond to the NPC's pose appropriately.)
2. Damaging vehicles
If the plan is to begin work on heavy weapons next, this should be done alongside it. In my opinion, the entire -point- of heavy weaponry is giving you the power to fuck up vehicles. Don't like the aero harassing you from above? Get out your bazooka and SHOOT IT DOWN. Big shot trying to get away in a car? Use your machine gun to blow out it's tires and windows. Heavy weapons and vehicles are intertwined with each other, so to work on one, you have to work on the other.
3. Vehicles damaging
Of course, you need a way for vehicles to strike back. Now, I don't know about cars, but I have thought up ALL SORTS of aero attacks, including hovering over someone and BLASTING them with vector nozzles. I can see the dangers involved in giving someone a big, armored weapon, but as long as every attack done by the vehicle damages it a little, I think you'll find people will be very hesitant to use the new feature unless they really have to.
This is something I've noticed myself and a couple others doing. Why put your vehicle in a garage when you can just as simply park it out on the street? I think that should start coming with penalties. In Red, that should take the form of gangers fucking up your ride, while up top, you run the risk of getting fined or even towed. This'll make people much more careful about where they leave their precious wheels and wings.
This is much less important than the other things I've mentioned, but it would still be cool to be able to customize your ride. What this feature would do is make car/aero parts like clothes, allowing people to make custom sides and bumpers. Alternatively, this could work like spray paint (sprayed onto %v is....) Personalized vehicles would be really cool.
People can get dirty, why not vehicles? Maybe it'd be hard to code, but it would add to the general immersive experience. It's also another job op (see Dirty/Clean places)