I'm not seeing the diminishing returns here. The value of a system to move workpieces around the shop multiplies the value of every machine in the shop. And if it can reach piles of stock and the 'finish' bins, it can move stock in, and finished parts out of, every machine. And it can move stock between every machine.
So, I see a track of ceiling rails running around the shop, and a couple of different carriages sharing the track, with different kinds of robot arms. As expensive as a couple of regular machines, but it would make a dozen existing machines capable of SO much more versatile use.