Bottom line, I've seen plenty of evidence that flatwound players keep their strings on much longer. Again, no surprise, since they like the sound. But that doesn't mean that the strings actually do last longer.
Everyone should play the strings they like for tonal reasons. The economic argument makes no sense to me.
Again, I tend to agree. I think the sweat/dirt/whatever argument is just rationalization with no basis. Every player's body chemistry is different, not to mention their eating habits and environment, so every player exposes his/her strings to different combinations of humidity, dirt, sweat, BBQ sauce, you name it. I don't think there's any way to quantify differences, nor do I think that time and effort in such an endeavor would be justified.
if you LIKE the sound, play the strings. You don't need to justify it to anyone. To me, strings "last' until they break. Up to that point, they're just strings doing their job. If you like the sound, play them. if not, change them.
And I'll leave those old flats (installed in 1972) in my '63 P just as long as I continue to like them - or until one breaks.
The original factory rounds on my 2000 MIM Jazz are also doing just fine, as are the flats I installed on my Univox hollowbody about 6 years ago, etc., etc.