I am playing a prince level game and was barely keeping-up with one of the AI on tech (they were usually 3-4 ahead at any given time). Then I built a wonder that generated a great merchant.
I played random settings and am on a large Pangaea map. I was also in good standing at the time with all the players, so I sent my merchant to the other side of the world to the largest capital I could find. Score, 2,500 gold or so. I was then able to set my science output to 100% taking the huge financial losses and I am now ahead of the closest AI by 3-4 techs. I just sent a second great merchant and now have nearly 5,000 gold and it's still only the Rennaisaince period. Woot. I see a domination victory in my future since I should have tanks by the mid 1800s.
This is what I like about the civ game. You can always find new ways/paths to victory. Right now I love the great merchant.