It would be nice to have something like collector's coins added, in short....
make the jewelry stores scripted businesses - they should sell for example:
jewelry -2000$
jonny's teh pope gold coin - 5000$
silver coin - 3000$
copper coin - 1000$
now the point is the prices would dynamically change after a period of time...so you could buy 10 silver coins for 30,000$, deposit them in the bank (assuming you could lose them after dying and it could be looted just like money) and wait till the price changes, sell it for more, or wait till it changes, buy something for a better price, etc....
this would be most suitable along with the business stock system, and the value of jewelry shop would need to increase of course..