I have a question about the commerce tree. It usefullness seems to limited to a very narrow type of naval game. I adopted it a few times when I was a beginning player, thinking it would really give me a great gold boost, but it never did. It seems to be sort of like Honor, not terrible, but other SPs just give you considerably more, and that seems to be the bottom line. In a game where you may have scarce SPs, you need to get the most out of them. In what scenario would Commerce actually be a better choice than Piety, Rationalism, Freedom, or even Tradition?
Some have mentioned, and I agree, it would be nice to see the benefits of the individual SP trees be more evened out, so there would be more choices. As it stands, there is no arguement that to complete the Liberty tree right off the bat is the best play. Honor and Commerce just don't compare.
The value of the Commerce tree is mostly in the Mercantilism SP. I've been playing around recently with a strategy where I build my capital up using Tradition, and then in the Middle Ages start expanding and buying infrastructure in newly founded cities with all the gold that the capital generates (Commerce opener + National Treasury + Monarchy), discounted by Mecantilism. For an investment of about 500 gold (Granary + Aqueduct) combined with the Tradition finisher you get cities that grow one pop every 2-3 turns. It works well on King, so now I'm taking it up to Emperor.