1. Whipping granaries & cottage spamming. It is better the hiring merchants: 1 merchant only gives 3 coins, while 1 river cottage gives 2 coins immidiately and the same 3 coins after 15 turns, plus it still allows us to grow.That's an amazing time Obormot. How did you deal with the economy problem? Caste system?
2. Despite working some cottages, I still had a negative GNP for the whole mid and end game, but I was getting lots of money from capturing more cities. For example, lets say I was loosing 50 gold per turn at 0% research, but I was able to capture 1 city per that is worth about 100-150 gold each turn. I won't go on strike and would even be able to afford some research. That way I researched construction at about 0 GNP, burning gold I got from plunder, and I researched CoL with negative GNP.
3. I extorted Currency from somebody, and sold some techs to the less advanced AIs. That also helped a little.
4. As I said I delayed capturing crappy cities from the AI untill later, and took out their best cities at first. I also settled a lot of cities to push myself over the limit in the last few turns. My economy was OK for the most part of the game (i.e. loosing less then 100 gold at 0%

But You do have a point about Caste System. The gold that we get directly from merchants is not important, but getting a great merchant quickly and using him to get money may be a good idea.