Copper should be a strategic resource early game (representing Copper Age weaponry). To be honest since an entire Age of mankind is called 'The Copper Age' i havent understood why it was removed from Civ up until now, especially as Copper is emerging again to be one of the most important metals on the planet. I would love to see it as a strategic resource in the early game, then being unimportant in the midgame and emerging again in the late game. It would make a very interesting mechanic.
As far as Truffles go, they don't feel worthy of a spot in Civ to me. I know they were a delicacy in middle-age europe but I feel Tobacco has had a much more widespread impact. Tobacco has been one of the most heavily traded resources since the Colonial period through to the modern day.. Also Tobacco as a Central America/ Carribean resource would represent a region that hasn't gotten as much attention in the game yet. Tea would be another better alternative. Tea was the reason behind the search for the North West Passage, the East India Trading Company, etc Both resource were FAR more impactful on the world then the Truffle.
I like the mercantile states providing manufactured goodies (porcelain and Jewelry), seems like a cute way to make them relevant to the game. Tullips on the other hand seem like a cheap cop-out to give the Netherlands a means to stay important to other Civs. The tullip has little value as a trade resource, it can't be eaten or manufactured. We're obviously going to keep the Netherlands alive as they continue to supply us with a Tullip and the happiness bonus that comes with it but it doesnt make any realistic sense.