I've never thought the "generic fantasy world" made much economic sense. Once you can teach someone to throw fireballs, why are they not directing that energy into a steam engine or something similar? Why don't you see kids at the mage university signing out a golem and two teleport scrolls to go help the family plant the summer crop? Blah blah silver, except with all the magi who need to practice these spells, that should be dirt cheap on campus.
When you get to replicator level, the currency is replicator bits. Heavier elements like gold will be worth more than compounds like water. Will it be some Star Trek utopia? Of course not. But if you didn't have to work to keep maintained, what would you DO? Of course some folks would destroy themselves with drugs. I guess I'm am optimist since I think most folks wouldn't.
RE: Generic Fantasy
Sometimes, when you give people what they expect, there is no growth. If a few trainee mages can levitate heavy blocks into place with magic, why would that otherwise inventive peasant over there bother with creating a crane? No need for a refrigerator when you can cast some type of freeze spell and make it permanent.
Lastly, and perhaps most cynically, "human" nature. Those that make the rules will ensure that those without power don't gain any. If that means demanding that the mages pay a tax on spell use - explaining the ridiculous cost for contract spell casting in most games - then it's in the ruler's interest to do so.
I remember this book I read in middle school about an earth on the verge of WW3 that sent a ship to a nearby habitable planet with DNA and the ability to grow humans. The ship was also staffed with robots for instruction and construction. They didn't have money but did everything in the pursuit of self interest. I might manage a nuclear reactor during the day but cook soup for people at night - free of charge. Why? Because nuclear physics interested me and I was a natural leader but my love was cooking. The catch is that this unique society developed when the robots programming got a little scrambled and they failed to indoctrinate the kids being raised on the ship. Needless to say, it was a shock for those that eventually made it to this new world from the remains of WW3 ravaged earth.
But the key is that this society came into independent being. I'm not sure you could ever create such a civilization from where we sit today.