Hi, I'm here to talk about the elephant in the room, that there's no way to win w/o owning the hell out of the industrial expansion tech branch. Here's some alternatives
Independent "Social branch" that advances as scientific output is accumulated regardless of tech choice. Periodic breakthroughs may grant bonus planetary production based on raw prod. regardless of how it's allocated. That way civs will just accumulate boosts really gradually, as more techs are gained.
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Have other tech branches give passive social production bonuses: thus, Terraform type sciences unlocking ways to "use existing planet structure for infrastructure", Science types "increase fabrication efficiency", Engineering types... kinda obvious, but they each would grant a percent based on final net manufacturing (not base manufacturing), again just to gain boosts gradually.
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Have other sciences grant onetime use bonus resources. Like trade goods, but they appear on a planet every x weeks as the population discovers/develops their colony, and can halve the cost of an improvement, for example. Eg "useful rubble" has a 10% chance to appear each week when you studied 3 research type techs. After 4 techs, it will appear on one planet every 2nd turn for e.g. This system has a wide range for possibilities, and will require thorough testing, but I feel it's the most creative solution to not having anything because you don't have that 3rd tier factory discovered yet, and enemy ships breathing down your neck.
When the next improvement is built then "Useful rubble" is consumed and 1/2 the build cost is added to the next item in the queue similarly to production overflow. *none of the above systems call for revising building costs. The only exception is that 'player achievements' and 'galaxy achievements' should not get these bonuses, so we can keep things from getting crazy.