As I see it, utility is related to what the multipool algorithm expects the shares to be worth ahead of time, while efficiency is related to what their real worth turns out to be after the fact, once multipool knows how many coins it will actually collect for them. Confusingly the two are not expressed in the same way, one is expected total worth, while the other is real worth per share (both in relation to the average worth of one share at the current difficulty).

That's what I suggested should be changed, so that you'd have "expected worth per share" and "real worth per share" instead, allowing for a direct comparison. If the algorithm is correct, these numbers should more or less converge over time.