Every bar of iron is a special and precious commodity. every block of obsidian, copper, silver and kimberlite is special, because without it, your craftsdwarves would make platinum piccolos 
See, I hold a differing opinion. I do my best to try to steer the crafters in to the most expensive components; I'm never in a critical shortage of, say, aluminum, so it's not a problem. I had a crafter make a Steel crossbow, with Blocks of native Aluminum; I considered this a great success. I love added wealth.
Personally, I hate added wealth by artifacts. To see my fort of about 400k wealth suddenly make a 1mil adamantine artifact makes everything else seem worthless. That, and I believe more wealth=more goblins.
But when you think about it, isn't that the way it is? If a fort produces a thousand masterwork steel swords, then you'd have a reputation for good swords, people would come buy your swords. If a fort produces one singular piece of work, a solid gold blade inlaid with precious stones and with craftsdwarfship beyond any other...
Look at it this way, then. Renaissance era. In three centuries, there must have been thousands of individual pieces of art created, buildings, portraits paintings, sculptures, and what have you. But you don't REMEMBER the white noise. You remember the Mona Lisa and the Sistine Chapel paintings, and you remember da Vinci and Michaelangelo. If you make something good but not great, it fails to rise above the crushing seas of mediocrity. Only by creating a work of art so great that people centuries later are still awed by it do you really distinguish yourself. So yes, it makes perfect sense to me for one artifact to be worth more than the rest of my fort put together.