Oh, I really like Sitzkreig and Sixxkillers' suggestions btw, so repeating them:
7. Fast Dive inherent plane ability for the P-47 (+1 card when diving).
8. "Armour" rating in the plane statlines. Armour 1 modifies damage against that plane by -1, etc. This would also help negate some of the brutal wingman attacks problem (Wingmen with attack 4 and +1 damage are OUCH! )
9. More planes (Hellcat, P-51B, Avenger, B-17G, B-24, B-26, Typhoon, Tempest, FW-190 armoured bomber attack model (with armour rule, above), can't remember the model numer), TA-152, Me262, P-80, Gloster Meteor. Forgive me if some of these are already in, only been playing a few days!
The existing system is a really elegant representation of the differences in WW2 planes, so I guess I'm saying that anything that gives the planes more 'individual flavour' while retaining good balance and game mechanics is a great addition
Jets may need a new special rule, maybe a 'vertical roll' ability (can get this for any card, like Scissors on agile planes) that would simulate the typical jet attack of zooming in, strafing and zooming away