Issue
Limiting each affinity to 3 era stars means that a player focused on a few affinities would have to artificially hunt for the other missing stars. This degrades the game experience in a couple ways:

  1. We're forced to become generalists every playthrough to allow us to hit multiple affinities at once. This causes all our games to feel the same, hurting replayability.

  2. We're forced to go out of our way to start unnecessary fights, or attach unneeded territories, or go through some other detour just to gather more stars. The game dictates to us how we should play, harming the role-playing experience.


Recommendation

Increase the era star limit from 3 to 7 per affinity. The current bronze-silver-gold system should remain for the first 3 stars, then any stars beyond 3 should be shown the same way extra stars are shown in the Contemporary Era.


With the limit at 7 stars specifically, we allow even the most specialized empires to still be able to move on to the next era, without forcing them to go for unrelated affinities.


Extra stars in certain affinities could be exponentially more difficult to achieve, so that specialized empires have an advantage over generalist empires there (otherwise, all we're doing is giving generalists even more stars to casually stumble upon). For Scientist stars specifically (where gold sometimes means all research has been unlocked), extra stars could be unlocked based on science per turn or total science generated so far.



While this seems like an inconsequential change, it would really open up specialized playthroughs. For example, we could choose to go for mainly Agrarian cultures, even if it harms our science or money or other aspects, and play a more lopsided (more fun!) empire.

The increase in era star limit means that we can continue to gather fame by playing our specialized empire - ideally this would add some variety to our games as we end up specializing more often.