Berry have you tried doing the following.
Go into your analytics account and go back to before you lost the traffic (you do have an analytics account?).
There should be at least one but probably many points where you see a steep traffic decline. Go to moz's Google update page and mark in red the points (on the anaylitcs graph)that you see the steepest declines. compare these dates with what Moz is saying in it's updates page and then you will get a clearer understanding of the creature/creatures that are hounding you.
I do this when I start with a new client it puts into graphic form exactly what is happening. you can then post the anonymous data here and we can all have a go at guessing what beasts are attacking you and giving you a better strategy to fix the problem
At the moment it kind of sounds like you are focusing on what might be but at least by doing what I said above you can get some sense of the definite.