So this begs(?) the question: Our brains pleasure circuitry is the ultimate arbitrator on whether an action is "good" [y/N]?

I would say that our pleasure centre is, like our words-feel-like-meaningful, our map-feels-like-territory, our world-feels-agent-driven, our consciousness-feels-special, etc. It is a good enough evolutionary heuristic that made our ancestors survive to breed us.

I am at this point tempted to shout "Stop the presses, pleasure isn't the ultimate good!" Yes, wire heading is of course the best way to fulfil that little feeling-good part of your brain. Is it constructive? Meh.

I would trade my pleasure centre for intuitive multiplication any day.