OK, in fact historically Bigger hasn't ALWAYS meant better or more powerful. Today, Switzerland, Luxembourg, The Netherlands, Japan and Great Britain are all very small nations-in size-but are very powerful in one way or another, be it economically, culturally, militarily or technologically. By the same token, lots of very large nations, such as the Roman Empire, USSR and Phoenecia-bot to mention The British, Spanish and Dutch empires-have all reached a height of power, then collapsed, either from within (internal revolts, economic failure and seccesions) or from without (invasion by other powers, individually or collectively and disease). So, from a historical AND gameplay basis, the Snowball Effect has always been a very bad thing-if only because it makes the end game eras so pointless and boring (you have either won conclusively, or are losing badly, so there is nothing left to do but quit or go through the motions

!) Of course, it is important to point out that corruption had little or no effect on the Snowball effect anyway-and was a cure which ended up being worse than the disease

!
Now, just based on what we know already, I can see several things that will help to alleviate the Snowball Effect-even without corruption:
1) Stacks of Doom will no longer be an effective strategy. Unit promotions and special abilities in certain terrains and against certain units seems to indicate that 'size isn't everything' when it comes to combat. The ability of large nations to pump out lots of units-thus ensuring further conquests-was a major contributor to the snowball effect.
2) Culture requires investment-no longer is it 'more cities=more cultural improvements=more territory'. Now, you need to choose to INVEST in your cities cultural strength and unity. As culture also now effects happiness, health and defense (as well, I hope, as effecting your trade and diplomatic relations). Then a warmongering nation will find it hard to both expand his nation willy-nilly AND hard to sustain what he already has. It also will force him to make difficult choices-invest heavily in science, or divert it into culture-or a balance of the two? This is why I so strongly support a Strategic (non-unit based) espionage and religion system, as it adds in even more of these spending dilemmas into the player's thinking!
3) City specialization. When every city of every nation is virtually identical, then it really does become a question of 'who has the most cities?' In this game, though, it seems that cities-and even whole nations-can specialize: maybe as commercial hubs, technological power-houses, industrial centres or breadbaskets, just to name a few. If this bears out, then it means that how many cities-and how much land-you have is less important than how that city evolves, and what kind of terrain and resources they control! Of course, if terrain improvements now come with a cost as well, then so much the better for reducing the Snowball Effect.
4) Civics. One thing which helped The Snowball Effect was the government system-IMHO. Wanted to be at peace? No problem, just be a Republic or Democracy. Want to be at war? Just become a Monarchy or Communist State. It didn't matter how many new governments got added, it really boiled down to a 'good at war, good at peace' dichotomy. Worse still, as your government choices had no impact on any other nations' relations to you, then you ultimately found every nation in the game being either communist or democracy. Civics really does seem to tip this whole idea on its head which, in turn, should help to eliminate the easy decisions that are behind the Snowball Effect.
So, you see that-if I have read things right-there are already plenty of ways that civ4 will impact on Snowballing-and thats even if no disease or civil war model is included in the game-or even if corruption and pollution are gone for good (with nothing to replace them!!)
Yours,
Aussie_Lurker.