@ CK MacLeod:
Buchanan argues that the stability of the unit of account should be one of them – that the entire system would function more efficiently if everyone’s financial calculations weren’t subject to radical aggregate revaluation.
If that's what he's arguing I agree with him completely. Where I have an issue is his (I assume based on your piece and the foregoing discussion) belief that an "independent" group of bureaucrats can be expected to be more trustworthy and wise in managing the money supply than the market will be if the fiat currency has to be backed up with reserves of a commodity ala the gold standard.
The political class and the public "economists" still believed in the 1960's that government bureaucrats could better allocate resources than the market, hence the experiment with wage and price controls ala WW2.
Currently the political class and the public economists still believe that the money supply can be better managed by government bureaucrats than by the impersonal market; but the market keeps on keeping on biting them in the rear. Eventually it will bite them in the rear to the extent that it did during the Great Depression which was arguably worse by far than the panics and shorter sharper lesser depressions and inflations that plagued the gold and silver years.
One nice thing (for the political class, government bureaucrats and unscrupulous "investors" who subvert and ultimately own them) is that control of the money supply allows them to make such depressions and inflations relatively painless for themselves while they work to increase their power. Until common folks realize what is happening and rise up with pruning hooks to upset the whole system.
People in general come to have reason to hate it when that happens, of course.
The "bad" thing about the gold standard was/is that it prevented all wise and all just governmental experts from playing money value games. We've long been off the gold standard; but there it (gold) is still, inhibiting governmental experts from playing money value games, it's trading price serving as a check on the real value of fiat money.
Control of the money supply corrupts. Absolute control of the money supply corrupts absolutely.
If I understand your understanding of Buchanan, he believes that a new "independent" controller of the money supply can be constituted which will be capable of resisting the political pressures that have corrupted the previously constituted "independent" controller of the money supply.