Guns are anything but pointless. If you can outrun zombies, then using a gun is definitely not a bad idea if you're in a sticky situation and can't do anything else. Same thing goes if you have enough ammo to kill the small group around you and then leg it before more zombies arrive.
On cars, I'm pretty sure they weren't meant for traversing condensed urban areas, but for long hikes in the wild or on the highway instead. Go to Muldraugh/West Point with your car, hide it in a safe place, bundle up some loot and then go back and retreat for another 3 weeks into your lonely cabin in the woods. Kind of makes it even easier to become a farming cabin hermit, so that's kind of a reason for me (or anyone that doesn't like being a farming cabin hermit) to not use them.
Using it like a tank and rolling up on a main street with your fully loaded crew might be fun though.
