There is a BUG option you can enable that shows you in the tech tree which era any given tech belongs to. Why isn't it enabled by default?
Anyway, can we do something about culture? It's not quite as useless as earlier with the new border system, but it still has the fundamental drawback that its effects are purely local while research, gold and espionage are all global. I have several suggestions as to how this could be addressed:
1. Maintenance reduction: More culture means more loyalty to the ruler, which means your citizens are less likely to actively work against you and are easier to organize. Reaching a new cultue level could reduce city upkeep by a certain percentage, and maybe reduce inflation by 1% as well.
2. Happiness: Reaching new culture levels could provide a "We enjoy the fine arts" happiness boost.
3 Golden Age: A variation of Civ5's golden age system, there could be a counter for global culture across your civ that launches a Golden Age once you reach certain thresholds.
4. Influencing other civs: Having a lot more culture than your rivals could make life harder for them, by making their citizens unhappy ("Other civilizations are more cultured than us") or increasing their inflation. Perhaps this should only apply to civs you are at war with or civs that have on average worse than cautious relations toward each other.