That would be 10 full sets of gear every week?
If I had only 10 items on my retainer, that would be 100 materia I could generate per week.

If 1% was rare materia, and 10% was uncommon, I could be looking at, at least 2M profit per week.

I'm not sure it is safe to do that in the economy, and would need a lot of tweaking before such a thing could be done. Also it breaks a few 'rules':
1) The spiritbond happens when you 'use' the item (your retainer is standing around not doing much, so is not really using it).
2) Spiritbonded would mean it only spiritbonds to your retainer, so when she gives it to you it should loose the spiritbond ^.^;

But otherwise, it would be interesting to have more things for them to do... but... then they would not be retainer, and more of a 'companion' or 'worker' or something? Which leads to a whole new mechanic.