Here's an interesting thing I discovered by accident. I had the largest junkyard on a big 64 square lot. Of course, since I could no longer salvage, it was useless so I bulldozed it. The next day I had a Sim where the lot used to be, looking for gems/minerals. What she found was a bunch of already repaired "salvage" items. Six of them including an expensive tv. Now, I haven't tried putting the junkyard back and doing a rinse/repeat thing but it might be worth a shot. It seems when I bulldozed the lot, the spawners stayed behind only they produced repaired items.