On an earlier thread on this subject, someone who sounded like he knew his business said the Grand Mighties undergo 26 separate forging processes.
The 75's undergo significantly fewer, the exact number of which escapes my memory right now.

What else would make one crank worth more than another, or, if not worth more, what would make one crank COST more?

Well, I don't care too much about finish.
The "champagne" finish doesn't appeal to me.

However, true circularity and in-plane precision matter.

Lightness matters, if strength and stiffness go along with it.

I would like to think that the Grand Mighties come out stronger and lighter for the 26 forging steps, and that Sugino makes fewer of them on better machines with more experienced workers, which would make for a lighter, stronger, more circular and precise crank for the money.

But I don't know that for sure.