A possible path to explore is that colliseums (and circuses) become less effective, or even obsolete, at a specified age. This would then require the more advanced buildings to be built, which would become less effective, or even obsolete, at another specified age.
The newer aged buildings are more costly to build than their older cousins, thus spamming small cities would be difficult to maintain as your age progresses.
This would also add some of that realism that people are concerned about, as it would be representative of your civilization maturing and evolving, requiring more sophistication as the ages progress.
Colosseums became obsolete in time. Circuses are still around, but are hardly the source of entertainment they once were. Both could become obsolete (or change to a +1 or +2 gold producer so the building is not wasted) when you are able to build...
Theaters (as implemented in the game) are present today, but are considered more of a source of culture than happiness. Maybe this would be its next progression (similar to how the above change to gold) when you are ready to build...
Stadiums are flourishing today.
To me, it all fits together nicely. It makes historical "sense" and thwarts ICS as an exploit. Those that wish to pursue ICS need to accommodate their population's new needs as they evolve.