The wrecks sort of nerf vehicles, because they create such congestion in the towns, it's not as easy to hop into a truck and mop up town with it's fender anymore. On that note, I'd like to see vehicle collisions less buggy. Hitting a car with your car creates this bizarre billards situation with vehicles blasting off at mach 9 on impact and slamming into each other and bouncing back. Crashes the game sometimes too.
The wrecks should be more like piled up, tangled and impenetrable messes your vehicle can get stuck into.
Now that we have wrecks everywhere we kinda need more variety in vehicles and the existing ones should probably be redone. Bear-proofing the flatbed comes to mind. Might need more kinds of enemies that can pose a threat to a player in a vehicle, or make vehicles vulnerable in a way to typical monsters. Not sure how though, maybe masses of zombies slow down the vehicle more, or vehicles lose traction/ control on all the slippery, slippery corpses. Zombies might be able to break windshields and doors better, hitting zombies at ramming speed might blind the driver, or their bodies go through the windshield instead of under the vehicle, or pull the player's arms off the steering wheel, I dunno.
Using vehicles to run down zombies is immensely fun and should be viable, just not as easy as it is now.
Also, unrelated thought, the world should get progressively ruinous and more difficult to survive in as time progresses. Maybe actually make it easier in the first season, then fungaloids and such things appear in the summer, roving hoards of zombies appear later, more threatening types of monsters appear. To keep the game fresh for long surviving survivors and maybe to make things interesting for the hermit-types that otherwise meek out existence in the wilderness indefinitely, trouble should go find players that don't look for trouble.