I'd say the ability to go into a random dungeon and stumble upon an artifact weapon or armor out of complete randomness and luck is much more rewarding and role-play friendly.
Not in my dice experience. If the GM spent considerable time planning and setting up a complex quest of campaign with planned high end loot, he would not present us that loot if we simply went exploring some random dungeon he didn't prepare for. Getting a lvl 40 sword at lvl 2 completely breaks gameplay, and I'm amazed how few sees that. A lvl 40 sword should be protected by lvl 40 creatures. It's there, but it's not for just anyone to claim.
Besides, artifacts should have more depth than being limited to weapons and armor, or some weird thing about that they *must have usable value*. How about if Umbra wasn't an ubersword but still powerful, but the artifact value of it was telling you a story about it through dreams or something, as long as you kept using it despite there being better swords in the game? That would work well enough for me.
How about they make you rich beyond comprehension, unfortunately nobody will have the cash for it's real value? Tempt also the collectors, rather than just the fighters.