Good feedback thus far. This won't be a simple solution. What would happen to the game if there was no caches? Slow it down?
If there were no caches or reduced resource income I would expect a few things to happen:
1.)
More infantry: First and foremost the manpower spent on caches would almost assuredly be spent on an extra infantry squad. Later in the game less fuel would mean less manpower spent on tanks. This in turn would allow for more manpower to be invested into infantry and support weapons.
2.)
A longer early game: Less fuel income would directly translate into slower teching and a larger window for light vehicles, light tanks, and even medium tanks.
3.)
Heavies will carry a greater opportunity cost: Currently it is possible to tech, build a number of medium tanks, and still have enough fuel to call in a heavy tank when the CPs are met. Without caches heavies will arrive at the same time but players will have to make a conscious choice to forgo or limit teching if they want to be able to afford a heavy tank the moment the CPs are available.
4.)
Tank losses will hurt: Since tanks don't bleed fuel like infantry bleed manpower it is possible for teams to acquire enormous stores of fuel once pop cap is reached. This in turn allows players to near instantly replace any lost heavy tank. With less fuel available loosing a tank will be a much larger blow.
5.)
There will be less explosions: Without munitions caches there will be fewer off map artillery abilities and plane strikes in 4v4 games and players will be inclined to use these strikes somewhat more tactically. The same will also be true of grenades and other munitions abilities. This will also mean that infantry upgrades will compete to a larger degree with off-map arty for munitions use and in turn make killing upgraded infantry squads that much more rewarding.