Well, isn't it funny to have Aqueduct built in Modern Age city? And what about Temple with its prehistorical Stonehenge look? I guess improvements should upgrade automatically over time (perhaps not temple, but church, not aqueduct, but a sewage system etc). Of course they should retain their cultural value.

The Aquaduct upgrades, not sure about the temple though, I dont look at my citys very often

I always thought it was odd that I had to build an Aqueduct in any city, as opposed to using workers to lay the aqueduct to bring the water from far away. Seems like the latter would be more realistic, but perhaps not balanced in terms of letting corrupt cities get aqueducts since its just a worker job.

In Civ3 at least, each improvement had a different picture on it depending on the era : granary would be a kind of a clay depot in antiquity, and a modern silos later. Aqueduc would be, well, an aqueduc at first, but a whole sewer system later, etc...

So it's already in the game.

Well, isn't it funny to have Aqueduct built in Modern Age city?

Huh? Aqueducts are a major component of modern cities. Look at New York, they have I think 20 huge aqueducts because they can only meet about 3% of the city's needs by pumping and filtration alone. The rest of the water is gravity-fed from huge reservoirs way out in the Catskills.