Update: a day after making the changes I detailed above the account has returned to normal and EPC is back to what it was before the downturn. Perhaps the most telling graphs I have are the ones for 'previous 30 days' with earnings and pageviews checked. They both sharply intersect and not for the better. Since last night they have switched back.
I could easily test the theory that your payouts are partly determined using account wide metrics by adding the units back to the games site but it has cost me a nice chunk of change already. Coincidence? The timing is too exact imo. Not only that but it happened to all sites in the same manner.
What else could it have been?