So after finally finding that Amulet on Friday, the game proceeded to give me lesser versions each of the last 2 days as well.
Just ran the Fields of Misery 5 times trying to find the Decaying Crypt so I could maybe find that bastard yellow Enraged Phantom. Stats:
Found Decaying Crypt: 1/5
Found Rare Enraged Phantom: 0/1
Got Key of Destruction: 4/5
Obviously that last stat made it worth it. I also happened to reach paragon 22 in the process, but I was somewhere within the last "bar" when I started.
I was not actively seeking the keys, but now that I suddenly have 5 destruction and 3 terror, I am kinda tempted to take a shot at the Hellfire ring. Still not gonna focus on that per se, but if I happen to acquire the remaining keys, I'll at least give the portals a run and see what happens.