... I say if you want to go to war, you must have some punishable consequence that goes along with it.
The "punishable consequences" are the happiness problem you get, when conquering too many cities (early game) *and* the diplomatic warmonger penalty which reduces your trading partners and finally causes mass-DOW (middle and late game).
I know that everybody has his own aspects, he loves about Civ. Mine (and many other players, I guess) favourite aspect *is* war.
Not, because it leads to an easier victory (I don't deny this), but because it is fun !
So, I don't think there should be more mechanism to penalize a war-heavy game, as this would probably drain fun out of the game (for "us").
What is needed, are new mechanism that bring *additional* fun (and not war related) aspects into the game. I would like to see this, too, as even for me, war is not the *only* aspect I enjoy with CiV.
Fortunately, this is exacly what seems to happen, with G&K: Religion, espionage, new CS-diplomaty - all new and promising non-war-features!