There is nothing the matter with the msp ecu.. There is a problem with people running 12psi or more, which btw is just 1-2 psi from max duty cycle for the injectors.
Look up what psi you can push before you start leaning out at WOT
Mazda should have put 370cc's in, instead of these whimpy little 270's. But they didn't.
I ran at 12psi all last summer, checked my plugs often, and i was a touch lean, not bad, but enough to make me back off to 11.
While the interheater we have isnt very effecient, and the ant hole we call a S pipe couldn't get a milkshake through, i cant see any resonable doubt that you couldn't run 10psi daily driving.
Motors don't just up and leave for no reason, sometimes its a factory defect, few and far between, but most of the time its driver error and lack of knowledge and maintanence when dealing with a FI motor.
Of course im not saying that replacing the interheater with an intercooler wouldnt help, and helping the motor push the exhaust out isn't going to help either, By all means do it, you'll notice a good feeling from your car when you do. it'll feel a touch more liberated.
But IMO its not mandatory to run a higher than stock boost level to a degree.