A cool way to improve, which also has a minor impact on end-of-content players, would be to have events like 50% off vehicles cost in credits. It would really help players on the bottom of the ladder and give them a small boost in growth when they're starting out, possibly leading to more players joining and continuing to play.
If it also applies to planes then it'll help players higher up the ladder and make it a little more feasible to have airplane squads.