True, you can import stupid amounts of gems, but hopefully that will change when the supply and demand effects get put in.
-and yeah, crystal magic is hokey, hippy crap, but dwarves are sort of make out of gems or rocks in the first place, depending on the myth. Why wouldn't a wizard with legendary skills and enough bags of gems at least be able to try to make replacement parts? It probably shouldn't work on humans, though.
Considering the hippy, tree-hugger vibe associated with crystals in our own world, it might be appropriate to make this an elf only ability. That would mean that adventureres would need to buy gems from the dwarves and carry them to the elves, to get their legs back. Seems kind of like we're tying an idea to much to the people who advocate it in our world though. Dwarves love gems; why can't they attribute magical properties to them?
What about good, old fashioned Hook-hands. How many of you love them? These should be the go-to solution for one handed soldiers, unless we can graft swords to the stumps.
Doctor Claw-sque hot-swappable hands for every occasion, would be pretty cool, and allow a dwarf to work again, even if his job normally requires a tool in each hand. A hammer hand for a stonecrafter to strike his chisel with would be a good start, but right now a dwarf doesn't need to hold tools at all, so that's probably unnecessarily complex.