Since no one has attempted this, I will.
Can you post photos of the spots?
I have little transplants growing and they have no spots, and I honestly don't recall having spots before. Maybe, I did and forgot? I know that I had spots after frost, but that was damage.
The Sweet Potatoes will make alot of tubers. The more vigorous the vine the larger they will get. But, you will get more tubers everyplace that it roots, that is why some are considering trellising them, so they have to put more energy into less quantity. They are vines, and instead of climbing fences and having holding tendrils, they run along the ground, rooting as they go, and they can be challenging to dig up, since they can actually go pretty deep.
I normally devote a bed, this year it will be a boat to them, and simply keep redirecting them, back into their growing area.
The leaves are also edible, although I haven't tried them.