An idea just struck me - why not, instead of making simply extremely fancy items, have possessed dwarves make truly unique items. For example, Dwarf Reg BeardGrabber is sleeping after a hard day of glassmaking, when suddenly he is struck by an idea. He runs out, grabs a sack of sand and a couple of various ores, locks himself into the glass furnace, and a few hours/days/weeks later, comes out clutching an incredibly detailed stained glass window. Inevitably, he can't remember quite how he did it, so it can't be repeated...
Of course, there would have to be limits - for example, could a bowyer or weaponsmith construct a simple arquebus? Probably not, although it does raise some interesting questions. Likewise, could this system produce capital? If books are implemented, could a dwarf 'invent' (for want of a better word) a simple printing press, allowing 10 or so books to be made at once? Or an improved bellows, which when used in a wood furnace, produces twice as much charcoal/coke?
Granted, this would take a lot of very careful balancing (and it would probably have to be a rare occurence), but it might add just a little extra sparkle to the artifact system. Just imagine your adventurer breaking into an abandoned fortress to find the legendary... well, the sky's the limit, really.