Ah, but Gold isn't some arbitrary commodity. Gold and Silver are Constitutional money - your Founders knew what they were doing.
Not to say that a commodity-based currency can't work. I think the BRICS countries are going to make it happen.
Just because gold and silver are referenced in the Constitution doesn't mean they're not arbitrary. If founders had added bronze or iron coins (like China had) or Platinum or Palladium it would have been just as arbitrary.
Right now the US Treasury and Fed jointly control the value of the dollar. With a gold standard, China and Russia would. That would be bad, actually!