We use a dolly simply because it was a cheaper option than replacing our new Civic which can't be towed 4 down.
Dolly Pros: more vehicles (as you have found) can be towed on a dolly, there is no extra equipment to buy, Storing at home or a CG is not the issue folks would have you believe - over half of it tucks under the rear of the MH, you can use a dolly for other purposes - I used to take quite a few friends' cars to the shop to save on a tow bill, in summary they are versatile and not set up specific to a certain vehicle.
Dolly Cons; it's much heavier to move around and there is more involved to hook up than bars, getting the vehicle loaded and centered can be a pain especially in bad weather, it's another set of wheels and brakes to maintain, the straps will need inspected often on your trip as they can come loose.
The backing up issue exists in bars or a dolly so there is no argument there.
4 down is MUCH easier to manage and maintain, but dolly's are far more versatile. But I wouldn't get rid of a car simply for the tow method unless I was full timing. Then it would be 4 down, no question.