Ordinary Success gains 1.5e on average (ignoring the extra action cost of the Counter-Creed for now; unfortunately the average is greatly dragged down by the Memory of a Shadow being unsaleable); Rare Success gains 52.5e on average (assuming Mortification of a Great Power is 62.5e, which is what its own page values it at).

Assuming a rare success chance of 7% (current experimental rate), this results in Provenancing large amounts of artifacts eventually converging on a gain of roughly 5.05e per provenance, assuming you have a Cabinet Noir to make the Mortification useful and don't mind the gigantic amount of variance. This is a very good rate, if you do it in large batches. (The EPA is a bit less than this, owing to the Counter-Creed needing an extra action to cash in.)

If you consider the Mortification useless, the gain is still 4.195e per. This is still pretty good.