yes, you can trade gold and gems and such "strategic" resources with other civs, but they cannot use them for antying because the resources have to be physically in a city's radius to build a mine/plantation.
My 2 cents, I'm playing English AoD, adn this is the first conquest I've played so I can't compare it to the others. I usually play random map games, and i never play anything less than monarch. My exp with this conquest has been more challenging than your guys, partly becaues I hadn't played any conquests yet so i didn't know how victory points work yet nor did i carefully look at the alternate tech tree... so my next run through, i'll do things differently at the beginning. neverhteless, i'm in second place with 8,800 vp's adn france has 11,000 vp's and a lot larger military. i probably have the best colonies because i settled first, but i was behind in techs through the whole game so i've been playing catch-up ever since.
My one complaint, similar to many of yours, is the lack of war. Now I have to admit, I normally avoid war as much as possible and enjoy other strategies, but for this strategy during this time period, there was A LOT of war; and I've managed to avoid ANY war in this entire conquest scenario.
-Brian