I can not think of any reward for achievements in he games I have played.
HiTech
Usualy it's a "secondary" or novelty/vanity rewards that doesn't impact gameplay.
Thought that come to mind that might work in the MAs (some with or without gameplay impact):
-Titles
-Airshow Smokes (black, whites and greys could be gamey - but neons or colorful ones)
-20k bomber airspawns over friendly HQ
-Fuel burn 1.0 or closer to it.
-More drones in bomber formations
-Different bomber formations
-A hot air baloon equiped with Mk103 turret.