OK, my new idea, just like the title, to increase the culture transmit rate gained by tech, maybe doubles the effect or even a little more.
1. the 5% increase of each research seems somewhat ridiculous. It really matters little, so once the player unlocks the culture center, it's not necessary to research the upgrade, since the effect can be neglectable.
2. Considering the fact that culture transmission "atteunates" severely in the space, the 20% (or 30% for Advent) upgrade really changes nothing.
3. on the other hand, there are 8 culture centers in one planet at max. It's different from the damage researches, you don't need to fear "the-first-wave-attack-kicks-every-ass-into-the-hell" pain.
Some additional notes:
1. I only mention the tech upgrade rate, not the initial rate. I just want to make the tech upgrades more reasonable.
2. I only mention the culture transmit rate, not the additional tactical effects. I'm afraid changing those will need more test for balance. Nearly all of my suggestions have the same precondition: the effort of debug and test shall be acceptable.
3. Maybe the effect of resistance research shall also be decreased, the current culture invasion is too easy to be countered, unless you are facing the Advent Loyalist.