Not sure why, but buying the Fancy Oil Painting (and I think I had the same issue with Solid Gold Rosary) doesn't decrement old silver coin count. Polo Trophy does appear to, however (my coins went from 4 to 1 when I tried and failed to get one after getting fancy oil painting). Am in run so cannot look into it further (and a hardware crash on my old mafia drive got rid my copy of the source for the boutique).