What changes does advancing to a new era have?

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?

Solution 1:

The following things change when you switch eras

• Potential new spy
• city state bonuses increases
• internal trade routes improve
• religious purchases increase in price
• policy trees unlock
• potentially unlocks ideologies
• As poland, gain a new policy
• affects world congress/UN voting system by making citystates worth more.
• makes it more expensive to buy influence with citystates

I do not believe that changing eras decreases the beaker cost of scientific research from before that era.