I would say it all depends on the "job" as well as the exposure the parts will see. It just isn't feasible for the average guy to go and buy a 1/2 pint of every color or finish to do a car. However, if its a "custom" job where say, chassis, underside and all components are the same color then it makes sense to buy a quart and spray.

I epoxy primed and sprayed all my suspension components, engine, tranny, etc. but I used spray bombs to do my seat frames.