Instead of having a star’s experience be cumulative, what if it were more like a tug-of-war between two states?
For instance, each star would start out as neutral upon initial occupation. From there it would slowly build a value. Once 1000 is reached, a “Peaceful” culture is established, and perhaps the star contributes in some small extra way toward Range, Banking, and Experimentation for its empire.
However, each battle a star experiences pulls the system into the negative. If -1000 is reached, the system becomes “War Torn” and the population contributes more toward Weapons, Scanning, and Manufacturing.
Of course this could be manipulated by allies who exchange aggression for the sole purpose of getting the military benefit. To prevent this: maybe a star resets to neutral (0) when it changes hands? Thematically this makes sense as well. The longer colonists occupy a system they become more entrenched in their way of life. If they are successfully invaded, it is likely that the people are eradicated and life starts over for the new owners.