A lot of MMOs and singleplayer rpgs actually automate the consolidation . Dragon age, for instance. WoW IIRC also did this. It needn't be nearly as invasive as some people may think. Usually it's some variation of a little symbol of a gold coin, followed by a number, followed by a little symbol of a silver coin, followed by a number, etc.
You're right, as long as this automatic consolidation is also implemented reasonably for the money, because I don't know any game where you can explicitly steal money in GP, SP, CP.
Perhaps money stealing should also be completely reversed and limited to items only. I always found it annoying to rob the merchants and then rest again because they had no more money to buy my loot so my inventory is empty again....
But since you brought up MMORPGs, I remembered @ Black Elk's suggestion to introduce a merchant with special currency.
Finally I'd like to see a dynamic where rather than collecting gems and jewels only to sell them for gold, that this would be inverted. The real value being the portability, ease of concealment, and broad appeal. Maybe there's a merchant somewhere, probably a Dwarf or a Gnome, who deals only in gemstones or jewels, and will trade higher value items and equipment for them, but won't accept Silver/Gold. That would be cool! I'd like to see a gembag and some visuals for the gems that make them look really impressive.
I find a special currency via gems difficult to implement. You don't find that many gems, because IMO they should be rarer than gold. Maybe you should work on a reputation system instead, similar to Brem from the Zhents. If it should be absolutely a currency, then perhaps letters of recommendation of the respective faction for side quests, which grant a certain amount of reputation points. These must be reached then, in addition to the gold amount of the item. But as I said, this would be MMORPG style and I don't know if that would be so appropriate or popular....
