Near the start of my work on Deep Field, I didn't have any upkeep mechanics for income. This meant that both A) you could have any number of ships, since your empire constantly produced them, and B) Your income tended to skyrocket faster than you could use it. I tried solving this issue with increased colonization and alliance costs, but it always felt a bit off. Additionally, the lack of a cap on the number of ships you could have meant that you tended to flip from being underpowered to overpowered, if the enemies left you alone for 30 turns too long.
Overall, it just felt bad. I realized at the time that there's a significant difference between how you should deal with local and global resources.
One of the core skills to learn in most 4x games is judging when to invest resources in a new colony, city, etc. These new resource producing objects cost a fair amount, both immediately, and over time: they take many turns to build up. Eventually they'll be worthwhile, but at the start, they do very little for you. However, if you can use a global resource to start or speed up the development of these new colonies, you can focus your whole empire's output on a small set of locations. This leads to significant and honestly unbalanceable increases in player power.
Deep Field has two local resources: Food and Construction, and two global resources: Income and Research. Research is internally balanced because I set the cost of every single researchable technology by hand. Income needed to be balanced, and I think I've done a decent job. Using a slider, you can set what percent of your Income you want to go towards maintaining fleets. Going from 0 to 100% fleet maintenance should take the player about 40 turns (if they have equal Income and Construction).
This means that they have to front-load the majority of the building time. If they're under heavy attack at 0% fleet, it's likely that they will just lose their entire empire. A player needs to stay at say... 30% to have a hope of defending themselves. And as they go up in difficulty, this number rises and rises. Still, they always want to keep it as low as possible, so they can make more money to start more colonies. This interplay makes for satisfying gameplay, and the short game lengths means that it isn't too frustrating when you gamble and lose.
Tying together the fleet cap and income, and putting in upkeep for buildings, stars, and fleets, has dramatically improved gameplay.
4x Lesson Learned:
Global resources need to be capped or limited in some way. A player's empire will change in size and output dramatically over the course of the game. Allowing them to focus the entirety of their empire's power in one location will end up being incredibly difficult to balance.