I haven't played Civ V yet. My current computer is not up to spec. I have read the that part of the manual, but that doesn't really give me a feel the mechanic. Hopefully i will before we get to governments.
Some of the vauge changes Geoff has proposed for trade sound sorta like Civ "culture". I don't think that's a bad direction to go for "trade". I wouldn't want to add "culture" in addition to the other resources we have.
definitely agree on using 'trade' instead of adding some new resource