In Empire Earth (the first one), I remember there being a "Standard" mode and a "Tournament" mode. The Tournament one was not an actual Tournament, but it made the game feel more like it was part of one. I REALLY think this could be applied to Civ4. What I thought was that Civ4 SP and Civ4 MP could have some different rules. Here's what I thought.

-90% War Weariness in MP
+50% Worker Production in SP

I got stemmed into action because somewhere I read that the reason why Expansive was nerfed in BtS was because Shaka was overpowered in MP.

Feel free to add more changes!

And simultaneously... What civilizations do you think need a bit of buffing of nerfing?