So I tried out this strategy:
http://www.colonizationfans.com/strategy/south-america-strategy.html

I made so much money I didn't know what to spend it on. The Inca capitol just keeps offering you 100 Silver for 50gc as long as you have 100 goods to sell them (tobacco, tools, trade goods, whatever)

It is great fun. If you want to be totally ruthless there is the path of then razing all their cities in the last days before game end to massively inflate your population.

As an aside, this works on any map that you find the Incans. Just so happens you know exactly where they are on The Americas map.