Regarding absolute phase/polarity, I would make two points:
1)It should be kept in mind that if a preamp provides a polarity switch, when the setting of that switch is changed not only is the polarity of the signal being inverted, but the circuit configuration that is being used within the preamp is being changed. In the case of a preamp having a balanced internal signal path, such as Ralph's designs, I would expect that to not be of much if any significance from a sonic standpoint, since the polarity change can be implemented in balanced designs by simply interchanging signal connections somewhere in the signal path. However in the case of preamps having an unbalanced internal signal path, I wouldn't rule out the possibility that the preamp's sonics could change noticeably when the setting of that switch is changed. Perhaps more noticeably than the resulting "correction" of the polarity of the recording.
2)I disagree with the notion of a 50/50 split, because I believe that for most recordings neither setting can be thought of as being correct. My suspicion is that on 90+ percent of recordings the whole concept of maintaining absolute phase or polarity is meaningless. The great majority of pop recordings, and the majority of classical recordings as well, are captured with a multitude of microphones (dozens in the case of many orchestral recordings), and then the signals from all of those mics are processed through elaborate multi-track consoles where they are mixed, equalized, compressed, limited, and subject to who knows what additional effects. The end result, when it comes to absolute phase or polarity, is inevitably in those cases a random hodge-podge of different sounds with different phases.
So if one setting of the polarity switch on a preamp sounds better than the other on a particular recording it figures to be more likely the result of random synergy and subjective preference than the result of the system preserving the "polarity" of the recording.
I therefore agree with Ralph that the benefit of a well implemented polarity changing function in a preamp will primarily be to the unfortunately very small percentage of recordings that are engineered using minimal/purist mic techniques, and that are engineered with minimal post-processing. But then again, those tend to be the kind of sonically high quality recordings that many audiophiles (including me) particularly seek out.
Regards,
-- Al