FWIW, my understanding of the "50/50 rule" is that it basically means that, on the average, the ultimate polarity of the recording (or any single track in it) is essentially random due to the many factors that Al and others have elucidated. That does not mean that some people hear a difference between inverted and non-inverted polarity. If it increases your enjoyment of the music, then feel free to flip whatever switch you want (even that nasty old Fletcher-Munson loudness contour). If it stresses you out, ignore it. ;-)
