Yeah, I just went up from 200 to 350 in weaponsmithing because I had over a stack of both platinum and mithril. Let your materials pile up and remember your characters share storage.
Oh, and trick: weaponsmiths use a lot more of their metal than their wood per level. If you create four of each inscription and only make a spear, a hammer, a mace, and an axe, you are being more economical about the more precious metal.