An example from Athens to work with

Indeed. I was mentioning something similar with the Theban shipyards. And I've discussed with @Emacz how much less monumental the Spartans were compared to the Athenians. Having different models could also be useful for any mod that wants to include building upgrades (civ allowing), which I've also proposed for Towers. These things would make civs more unique, and make gameplay more interesting.

A stone theater was not built in either Sparta or Thebes until Hellenistic times. Prior to that, both cities had wooden theaters. The current stone theater/sanctuary model can be used as an Atlas object. For base game, half of the Spartan Theatron's cost could be in Wood.  @Obskiuras, would you like to create a concept?

Don't forget hele_decor_spec.png in tropaion_shields.xml  

I don't think we have to reinvent every wheel. Explore avenues of improvement and innovation, sure, but the standard countdown timer has always worked perfectly.