I don't see a Constitutional problem with eliminating FRNs and replacing them with coins. The coins will be less convenient and still won't contain gold or silver, but if that's what we have to do to make the goldbugs happy, then I guess we should do it.
For God’s sake, how can you square coins without gold or silver with the Constitutional idea that nothing but gold or silver coin is lawful money?
Under your approach to interpreting the Constitution, if we outlaw everything except toy guns, that’s just fine, because we still have the right to bear arms—it’s just that they are made out of plastic and can’t kill anyone.