Is The Platinum Coin Legally Required?

It seems to me that the genuinely interesting legal question about large-denomination platinum coin seigniorage isn't whether it's legal (it clearly is) it's whether it's mandatory. Consider: 1. Under the Congressional Budget and Impoundment Act of 1974 it's illegal for the president to spend less money than congress has appropriated—the Nixon administration had this idea that it could enact unilateral spending cuts, but it can't. 2. Under the terms of the statutory debt ceiling, the president can't borrow extra money without congressional authorization. 3. I don't believe there's a specific statutory prohibition on collecting taxes that congress hasn't authorized, but this principle is pretty literally the foundation of the entire fabric of common law. 4. The Treasury Secretary can instruct the mint to create platinum coins of any denomination. On its face that leads t...