This question contains massive spoilers. If you do not wish to have your game experience spoiled, do not scroll down!
According to the Dwarf Fortress Wiki:
"Even if you kill all the angels inside a vault, they will eventually respawn (no confirmation yet about how long it takes--a cleared vault has been witnessed having its population back in under a month) which makes vaults pretty good high-level item grinding grounds."
You can embark at Vaults if you have DFhack (there are other ways, but this is the fastest).
If I avoid getting slaughtered by the Vault-Clowns, I could set up a way to kill them with cave-spider-webbed traps or catapults every time they re-spawn.
How good of an industry would this make?
I am willing to take the risk of !!FUN!!