I think the corp as Wonder is a strategy along with 4/city to reduce the likelihood of the economic/technological imbalance which players start to benefit from around ren/industrial era.
As far as balancing the game goes, and knowing that there is not the time nor expertise to heavily modifty the AI so that non-player empires can keep up, I'd suggest the following:
Seems to me the 'perfect-storm' runaway tech and economic imbalance issue is a combination of factors and not as simple as some have suggested. People have suggested getting rid of all new civics, removing Wonders, etc. But that sounds to me like Vanilla BTS a whole lot.
I think that the reason players get a huge late-game advantage is because of our abilities to recognize the patterns and put together a combined strategy to maximize the (admittedly rather large) bonuses from civics + wonders + buildings. So... all the new economic buildings for a seaport + plus a couple of key economic wonders (minaret, marco polo, etc.) + an early corp + free market = ridiculous money generated compared to AIs. Players see the pattern ("oh wow, this could be huge if I put these together") and plan to maximize their economies... I suspect AIs have no way of doing this beyond the vanilla BTS strategies provided by Firaxis.
Basically, AIs can't cope with the wealth of new combinations, buildings, and opportunities provided by RoM. Also, let's be honest, the Firaxis AI pushes the non-players to concentrate almost exclusively on making war, whereas in RoM you really do need a balance in the mid-game of economic/scientific so you can get far ahead later.
So... seems to me that there are a couple of ways to make the late-game balance a bit better. One, and I hate to say it, but some kind of late-game penalty applying only to human players (happiness/health/building seem easiest to code); two, increase production and research costs by at least 50% for industrial, 100% for modern, 250% for future era techs and buildings; three, reduce some of the resource requirements for bonus buildings, or make some buildings give access to resource.
The last point, about bonus buildings and resources, is really about the salt-stone-fish-meat fiasco. If you have access to salt, stone, at least one fish resource and at least one meat resource, you end up with bonuses by end of renaissance era that total something like: +15% production, +10%-+30% food, +3 health/city, +25% science, +10% maint +1 trade route/city +25% yield, and possibility to build a third +100% science world wonder. With a tiny bit of resource planning and a bit of luck, a tiny bit of building queue thinking (these are all cheap buildings as well.. butchery, tannery, glassblower, observatory, etc.), you can by the time you get to ~navigation in tech tree have an enormous economy running.
But, and here's the kicker... I'm not sure the AIs can see this, plan for it, or even if they do the salt/stone combination is rare enough that players can dominate it, park spies, etc. to ensure that only they get these game-breaking bonuses.
Solutions: remove the salt-requirement, make salt more common, make a building which produces salt, or something so that all civs have relatively simple access to this building strategy.