Andy,
I am very happy to have soft cloth and touchless side by side. If I had to choose to add a third unit, it would be an Odyssey. I have recently been to a training school held by D&S and have been amazed at the technology built into these machines. If you put in an Odyssey with no other compition in the area, you will have the leg up on the others. The soft cloth cleans very well and will sometimes clean a vehicle when the touch free will not. One very good advantage I can see with having both Odyssey and Quick Silver together is that much of the systems and technology are the same. Parts inventory and support would go hand in hand. If the Quick Silver was available when I was buying, I would have bought the pair.
Hope this helps,
Mike