Here's the way I would look at it... Lets say that the day after you bought your newer used car, some drunk runs your girl off the road and into a guard rail rendering it not drivable any more. If you have collision coverage, the car will either be fixed or totalled. If you have no collision coverage, you're left with the tow bill, storage charges if you don't have a place to take it right away, and a car that you can't drive, that isn't worth even half as much as it was before it got wrecked.
You may be a great driver and your skills may have gotten you out of some sticky situations many times before, but insurance is there to take care of those situations that you never thought could happen.
If it were me, I'd look into adjusting my deductibles to lower my premium, and maybe if it'd be the third car, take the rental coverage off of it, but I'd keep the comp and collision for sure.