I'm not sure about how much this is the case but I imagine that having a larger proportion of higher tech aircraft means that stats for older aircraft gets compressed to make higher performers more distinctive. I got this impression from trying to figure out a stat for the A-4.
A question about the pilots, are these individual characters or are they abstract attributes for all the aircrew on aircraft like the F-4? I'm going to try run my first camapign with 2 pilots on two seater aircraft and use the best attributes from either one.
As for some ideas

rocket pods for marking targets, could give +1 AtG to follow on attacks or good against soft target having multiple shots like chaff/flare.
Base/runway size and max aircraft size it can operate. Planes like OV-1 and OV-10 that can take off from short runways.
I can't remember if there's one already but recce pods should be vital for recon missions.
NOE flying to avoid RADAR. Could be another altitude but require a roll on a table each turn, Crash, Close call - climb or success.
Taking missions/campaign from adjacent region, aircraft starts with 5 less fuel, makes air to air refuel more important.