The rules are pretty clear that you can only trade resource cards. When they say things like "However, you cannot give away cards, or trade matching resources (

The rules are pretty clear that you can only trade resource cards. When they say things like "However, you cannot give away cards, or trade matching resources (“trade” 3 ore for 1 ore, for example)" and "You cannot trade or give away development cards", it's pretty obvious what the intent is.