Ben, I would not go as far as calling it a misfire, but take your thoughts on board. It is like a light flickering on and off quickly... the power is there, but not quite enough to be on constant.
What was physically wrong with the rotor arm when you traced it to it? If it was the rotor arm, does not explain why the problem resurfaced 6 months later (for me)....have spare to try...
I think the wire to the distributor that broke the likely cause as did not feel good when testing connection, and the spark plug breaking was coincidence.... Will see on Sat.
Paul, not around on Sun, give us a bell on Sat.