Its obvious intention was to centralise currency by preventing the states from making their own scrip. The Framers were perfectly capable of writing limitations

Its obvious intention was to centralise currency by preventing the states from making their own scrip. The Framers were perfectly capable of writing limitations on the federal government reflecting those on the states if they wanted to - look at the restrictions on bills of attainder and titles of nobility. And the first Bank was not set up by the Constitution - it was set up in 1791 by Act of Congress after a political fight between Hamilton and his critics. The Spanish dollar existed at the time of the US's founding, as did various other countries' (differently weighted) dollars; the US dollar wasn't defined until 1792 (when it was, indeed, defined as given weights of either gold or silver - the Spanish dollar was silver only). But the US dollar was defined by Congress and can be redefined by the same. And they have.