... Okay... so this is another "labor = wealth" argument. What if I use robots or my factory is otherwise automated?
Only if you define "labor" in the widest possible sense. Creativity, ingenuity and craftsmanship as well as design, and, of course marketing go into the equation as well.
Your robot factory is purely theoretical. There is no 100% automated corporation anywhere on this planet nor will there be in the forseable future. You can automate some of the manual labor, but not the design, development, research and marketing that are equally necessary to generate revenue.
But even if you'd accept the theoretical concept of a fully automated factory, there are still humans in the equation, as the managers and owners of the factory. Wealth generation can use tools, and it doesn't matter if your tool is a hammer or a robot or a whole assembly line.
It boils down to the same thing.
Yes, to the medium of exchange being an abstract concept. It doesn't matter if it's numbers or potatoes, if you use it as a medium of exchange, it is money, and as such it is abstract. It is abstract because the people who sell you something for a sack of potatoes aren't looking for ingredients for dinner, they are looking at the abstract monetary value of the potatoes.
The abstractness is not in it being printed paper or numbers in an electronic account, it is abstract because its value is not linked to the use of the actual physical entity. If it were, a dollar bill would be worth very little because you can't use it as note nor toilet paper and it doesn't burn very well, either. Likewise, if you'd use potatoes as units of exchange, the value of a sack of potatoes would very, very rapidly detach from the actual nutritional value of potatoes.