I don't understand the reluctance to trade iron. We wouldn't give away our only source, that's for sure. And if we want to increase the chances of other civs going to war, we need to keep them supplied with weapons. The Mayans are unlikely to take an agressive stance if all they have is archers and eveyone else around them has pikemen. Like mad-bax said, we'll have our own luxuries soon, so we might not want to trade for those, but if we can get techs or a good amount of gold, we can send iron to some far off civs and encourage military build up on the other side of the world.