I am looking for ideas, suggestions, or actual code to make various parts of Civ more realistic. Assuming BTS version, what would you or have you changed in your game so that it's a little more accurate?

Few early ideas:
Nukes destroy cities
http://forums.civfanatics.com/showthread.php?p=5863596

Nukes are researched independently
http://forums.civfanatics.com/showthread.php?t=238246

Global Warming
http://forums.civfanatics.com/showthread.php?t=145922

Unit Stack limit
http://forums.civfanatics.com/downloads.php?do=file&id=6853

others?

I've seen somebody's suggestion (actually - "how to") change usage of oil. Every turn your buildings/improvements/whatever generate some amount of oil resource, and your oil-dependant units consume it every time they make a move. Some consumes like 1 oil per move, others 2 oil per move and so. Basic idea is like this, I don't remember details. This is really far more realistic than default game, but I cannot tell if it's playable. I'm not a big fan of realism.

thats a great idea, but i'd agree, that's almost too realistic, lol