Just a quick point on the Holy City / Wall St issue raised earlier, as I think some confusion has developed.....
If you have the shrine in holy city, and have spread said religion widely, then almost always (I can't even think of a way this wouldn't occur), then your Holy City will be your best gold producing city. The shrine income is 1 GOLD (not commerce) per turn, per city, and therefore it isn't even a decision that takes a moments thought. You build Wall Street there, along with every possible financial development building.
In my current game, huge map, my Cuzco gets 84 Gold per turn from the shrine income (yes that's 84 cities I've managed to spread Buddhism to). At 100% Tax Rate, it generates 512 Gold per turn (that's with Wall Street et al, I haven't got Airports yet so it will get more

)
So if you have a widely spread relligion, with the shrine built, then Wall St is a no-brainer in your Holy City.........(though there are probably exceptions to the rule)..