As it stands right now the auto workshop isn't very useful.
I propose enacting some options to make it more viable:
Allow it to be used to scrap vehicles for parts.
Allow it to change the paint scheme of a vehicle.
Allow it to call a "used car" trader that you can sell/purchase cars from.
Allow it to be able to fabricate special, unique upgrades such as:
1. Machine gun turret that another player can utilize when they join your game.
2. Flame thrower, either similar to the Burninator or allow it to be turret mounted, or front or rear facing.
3. One or two additional cargo slots.