okay here's another stupid question. so the trailing plugs are they just for emissions or do they help on performance? just wondering b/c i replaced the leading and was wondering if i should change the trailing also?

Due to the long, thin shape of the combustion chamber in the rotary, Mazda uses two plugs to improve combustion. I would expect you could tell if you were running just the leading plugs.

leading provides the majority of power, maybe 80%?

wow that could explain why it seems like a pig lately. i'll change them out then.