Hmm... I'd say that value modifiers should be ADDED to the base value, rather than multiplied. Think about it - a well crafted gold goblet is not worth much more than a crudely crafted one, simply because the value of the gold itself overpowers the craftsmanship concerns. On the other hand, a masterfully crafted bone bracelet could be worth a fortune, probably about as much as a masterfully crafted gold bracelet, since it's the crafting that you're paying for, rather than the material. Would the Mona Lisa be worth more if it were painted on a gold canvas? Not particularly. What about that "painting" you did yourself, despite having no particular artistic skill? Yes - because the gold is worth something, even if your painting is rubbish.
Of course, the value modifiers would have to be changed to reflect usage with multiplication rather than addition.