How can you extend copyright to include such a thing?

Simple, you wouldn't. Yes, but this is already covered in the concept of sufficient creativity.

Also, pre-computer automation was not as impossible as you might think, some examples: A double pendulum with a pen, a spirograph, a sand bucket on a rope, a spinning top with paint.

Also covered by "sufficient creativity" for trivial combinations of such machines. Now, if it was a system which balanced the spirographs and double pendulums in a tangible and describable way as to produce a finely balanced effect.

And see this reply from someone else... generated artwork has existed before computers, and it is not copyrightable.

Yes, but the degree of automation we have today completely changes the technological landscape in such a profound way, that anyone should be skeptical if such laws still apply.

I have not completely decided if I would agree with your proposal or not, you would need to be much more specific about the limits of where copyright would not apply.

Common sense and the market could resolve a lot of the potential problems you see. What use is a tool like a spirograph if you can't use the output freely? Tools with restrictive stipulations will eliminate themselves from the marketplace.

Things like a program that simply enumerates all 32x32 pixel images are transparent enough that a judge should be able to adjudicate properly. I can see, however, that there would be more complex cases, and the cost to society may not be worth the potential damage IP meta-squatters would incur.