Oh I forgot.. sometimes stats are even an inducement to fly something different, as silly as that may sound.
I do occasionally look at my career stats and think "Oh, I haven't much kills in a XXX, let's make it a main ride this tour" or "Let's see if I can increase the 109G-2's K/D in LW MA by at least 0.2" 
(actually i look a lot at my stats...it's almost a fetish
)
Last tour, I tried to get a kill in as many different rides as I could. I managed to get kills in 61 of 96 possible. Even a chute counts - so proxies included unintentionally.
It got me into a lot of rides that are hangar queens, and made the obvious even more so that there is a preponderance of fast LW planes at high altitude - P51D, F4U, Typhy/Tempests - that love to pick away at low, slow birds.
Still, it was great fun and facilitated by the stats available.
On the scoring system for squads, I believe it is an objective and automated system. The logic is not obvious by the examples posted.