I would rather the retainer be used to do something unique, rather than just do what players can do, but crappier. Maybe be able to send them out, and they will occasionally come back with a rare doodad to be used in a synth, or some consumable with a unique effect, or a pretty rock you can put on a table in your new house. Someone was talking about letting them take care of your chocobo, or have them take care of your house, or go fight in the Colosseum for amusement and advertising purposes (big logo on the back for cheap darksteel! best prices in town!). Something players cant do on their own.

If they go out and come back with 10 iron ore, the crafter will be disappointed because its not enough to be worthwhile, and they will still have to buy more, the gatherer will be disappointed because they could have just gone and gotten way more on their own, and the fighter wont care and will just sell them anyway.