One of the problems with credits right now is that once the the player gets more than 10 million credits, there's no further use to getting any more of it.
A) I think the gameplay around credits could be more rewarding if there were more ways to use credits to boost existing activities.
For example, maybe the player can boost a planet's fleet budget with an extra 1-2 million credits a month, to greatly boost the fleet power of that colony in an emergency to counter a large raid. Or, let the player provide 1-2 million credits in material aid to an faction colony to boost the said faction's fleet power with mercenaries, so they can distract another faction the player is targeting.(Like boosting Tri-tachyon's fleet power to Vahalla, so that they can distract Rasaelvig's patrols, allowing the player to more easily send in a stealth raid)
Also, maybe make it so the average colonies can only reach stability of 7 or 8 even with all upgrades, and the player has to commit 1-2 million credits a month to boost the security budget of that colony, so that the colony serving as the player's main shipyard can produce better quality ships.
B) I think colony profits would be more rewarding if the colony's credit generation requires more of players' direct involvement. I think it should be balanced like trading cargo, where going at it peacefully the colony would make very tiny amount of profit or even no profit(like, cut export profits by 90%). Making large profits from having a colony should require danger and combat to keep the player involved and creating more gameplay. The player would have to work at it, shoot down convoys, bomb spaceports etc, to create opportunities that lets them sell the stockpile goods at a profit.