I really do not know when it makes sense to trade a vehicle anymore. It seems that no matter what you trade in, no matter how good it looks, dealers nowadays will try to steal your trade, even if they sell you a new vehicle at an attractive price. I am old enough to remember that if you traded a car or truck in 1980s and early 1990's dealers were content to make a $ 1000 profit on your trade and they assessed it accordingly. Today they expect to make a $ 4000 to $ 5000 profit (or simply put as much as they can) on your trade and they low ball you insolently on everything you try to trade in. It has gotten so bad that even Kelly Blue book seems to be rigged to maximize dealer profits. Just look at the difference between dealer retail and trade in value! And the same goes for motorcycles and other vehicles. i was absolutely stunned how little several dealerships offered me for a showroom condition 2009 Kawasaki Concours with 6500 miles!
It seems that if you have a vehicle that you like driving and it does not cause you much grief, hold on to it until it is worth no more than couple thousand dollars or so and then donate it to charity.