Previous BG games (and NWN games etc) also generally refrained from 'vendor trash' items like plates and milk jugs. These are the items that would benefit most from expanding the monetary system to include copper & silver, because as-is right now a large amount of the items you can pick up are valued at 1gp. Would be nice to see less compression in the prices in the game IMO.
And really, of all the traditions Larian has brought over to BG III from the older games, and all the things it hasn't....I have a hard time seeing 'BG I + II only used gold coins' as an unassailable sacred pillar of the OG saga.
