I wonder what shovels were worth after the Gold Rush faltered. Blacksmiths probably had all the scrap iron they could ever care for.
A key thing to understand about the gold rush is that it was not a major economic event, or at least nowhere near as big as the participants thought it would be, hence the tradegy.
The AI gold rush is different in that there actually is a mountain of "shovels" large enough to flood the global market quite severely.
Not sure what that means for the metaphor, but there you go.