All hail RoM/AND --
Seriously, if you haven't played the Civ IV Rhyse of Mankind/A New Dawn mods for IV -- you really ought to dl them and give them a shot because this is PRECISELY what they do.
Barbarian cities spawn into to civilizations -- it's nothing in AND for there to be 30 active civs, even late game.
In addition, the Revolutions option means that any empire that gets too large comes under rapidly increasing risk for a revolution -- so large empires rarely run and keep running away with a game. Inevitably, they run into bloat and the revolutionaries become more than they can handle.... leading to lots of smaller civs breaking off all the time. It likewise adds a lot of usefulness and more dimensions to religion and espionage -- you no longer have to just match larger opponent civs in size and strength -- you have a lot of other options to undermine them. I've held off Civs twice my size by simply focusing on diplomacy, religion, and espionage -- and cracking them into squabbling bits of smaller nations.
Conquest/Domination wins in RoM/AND are virtually impossible -- which makes it incredibly fun to TRY to win a conquest/domination game.
RoM/AND sounds like it would be right up your alley....
...and that's BEFORE you see all the wonderful other little goodies those mods have.