I tend to play the USMC a lot (what can I say, service bias here
) and yes, I find aircraft of questionable value in WinSPMBT.
This is for a combination of reasons.
1) The AI always has hordes of MANPADS. (Usually 2 to 3 times as many as would "realistic" in my opinion)
2) Aircraft are to expensive for the amount of damage they generally do. I won't get into how many times I've had 4-6 aircraft waste their ammo on a lone infantry squad that happens to be in the middle of a tank company. Not that there aren't the occasional (VERY occasional) successes where an aircraft takes out half and infantry company or some such.
3) Even with stand-off weapons I see an amazing number of hits bounce off vehicles ("You hit for 100+ penetration VS 5 armor, shot fails to penetrate").
All that said I still add them to scenarios for "flavor" if not anticipated effectiveness.
For pure "bang for the buck" by on-map MLRS or HIMARS, about the same cost as aircraft and generally 3 to 5 times as effective.
If you can afford the cost, and number of aircraft slots you're allowed in a given battle, using UAV's to draw fire until the AI runs out of ammo is a VERY effective tactic. Just fly them on your side of the map to draw missile fire but stay out of machinegun range.