As of now when I find certain types of items I get a lot but have no use for, like cell materia, or holiday spirits, I edit the config files to allow them to be refined into a small amount of pixels. So this is my work around for not having a way to salvage or sell certain things.
I get the OP's recommendation but I'm still a bit on the fence, it's a good idea but if you could salvage weapons they'd only give you wood and a metal bar or 2.
Ya it would have to yield something but not be overpowered returning too much of the base material, maybe 20% of original materials used. So if it took 10 bars of whatever you'd get back 2.
I think a good example of salvaging would be the system they use in Diablo 3, were you break it down into a component related to the weapons tier (common, magic, rare, legendary, blah blah blah), and if you have enough of those components, you can use them to randomly generate a new weapon of that tier. Obviously the specifics are a bit more in depth than that, but that's the basic idea for those who haven't played the game I'm talking about. I just think it's a good system, and worth looking at.