Ressuply tanks don't work on the driver, for whatever reason, so why would I buy them?
Also, what Threve said. This game is meant to have a bloated economy. You have 48k worth upgrades, 6k tanks, and any meaningful late game unit+infantry combos cost you 4k+ every time. Unless you're driving in an infrared all game, only taking engagements you're confident to win, you are going to die. And then, you do need that money.
For me, !ammo drops are crucial when i lose the war factory. When I need to be sneaky and preemptive with my infantry play, i can't afford the luxury of running back to base every time i run out. Making it more expensive (500 is the cost of another infantry piece, which is often difficult to afford in low-eco games), defeats the purpose of it altogether. If you want to nerf it (and i don't know why would you), increase the cooldown.