Traded my '10 2LT RS in after 37 months, 9000 miles. Tried to sell it privately for a year and a half, no takers. Another winter was looming and more depreciation the trade was the best option. I decided to buy a cheap SS for reasons you probably could care less.
My advice? You will get your head ripped off if you don't go through the trouble of trying several different dealers. Be patient, I went to 4 dealers and got 4 different amounts. When to do this? Do you have a loan on this car? I would wait until the loan payoff is less than they offer you in trade.
This was almost the point of no return here, I was wondering if I was doing the right thing.