" Of course it's the Crown rather than the Monarch her/himself that provides that stability so by all means stick a Crown on our coins if you prefer."
What exactly are you saying here ?
'The Crown' is symbolised by the reigning monarch, how a circular ornamental headdress provides stability escapes me. (Perhaps it would stabilise a wig.)
'Market forces' determine the stability of a currency not a monarchical system.
"By AD 800 coins regularly bore the names of the kings for whom they were struck. A natural development was the representation of their own images on their coins.
Coinage played a part in spreading the fame of kings - the more often coins passed through men's hands, and the further afield they were taken by plunder or trade, the more famous their Royal sponsors became. Athelstan (d. 939) is the first English king to be shown on his coins wearing a crown or circlet." - official web site of Lizzie's Royal Family
https://www.royal.uk/coinage-and-bank-notes
Some say advertising aids indoctrination, but I am not sure if 'commoners' would agree.