Judging from this question, advancing to a new era may have this effects:
- increased bonuses more from city-states
- unlocks policies
- makes your opponents think your are ahead in tech (at least in multiplayer)
- cities make more damages (or is it just the animation that changes ?)
But is that all (or true, at least)? I've heard in some "Let's Play" I was watching that changing era decreses the costs of past era technologies. Is that actually true?
There is a comprehensive list of changes you get by advancing to a new era?