"While Civilization might have better graphics/sounds, that doesn't add much to the "educational" value."
When I was a director of a summer "Computer Camp" in the 1990s, we allowed our campers to play Civilization II. Within it was a plethora of information on historical figures, places, etc... to which the campers were actively seeking out in the "Civilopedia" as they played. Seeing this engagement across genders and ages, was a key reason why I sought out employment at Microprose after college. (Disclaimer: I'm currently employed by Firaxis; opinions stated here are my own.)
Civ5 has built on Civ; each version has pushed the level of graphics and sound which a few have argued do add educational value as it makes the content more compelling; I agree.
The last few versions of Civilization have offered a great deal of MODability. You too can change game rules, UI, etc... by modifying XML and the supplied LUA. As for the depth of what you can do, check out this awesome WIKI fans made of the MOD system: http://modiki.civfanatics.com/...