I love this game! It's varied, fun, and just a little bit addictive.
I have a suggestion about the cultural buildings. My heroes have reached the Medieval Age. I just completed the research that makes the Totem Pole obsolete, and I think that makes perfect sense. In the real world, at a certain point the cultural artifacts of the past become obsolete--even embarrassing. But then, much, much later, they become important again.
What if those cultural buildings that we hang on to stay obsolete for a while, but then become relevant again after an age or two? I suggest that if a player has culture building at level 10 before it becomes obsolete, and they choose not to demolish it, then it could be revived later (The Totem Pole is revived in the Industrial Age, etc). Maybe just with the passage of a few ages, maybe after researching "anthropology" or something like that. The revived cultural building might be worth only half as many culture points, but it would still be worth something. The actual Coliseum in Rome doesn't have the same value to the city as it did 2000 years ago, but it still has value today.
This would affect game play by allowing the players who choose the inconvenience of keeping an obsolete building--and not being able to use that space for an active building--to make up for that sacrifice two ages later. Plus, those buildings are so pretty!