This is my line of thinking in your situation. If your wife doesn't like the car she has, it's not a matter of if but a question of when. Might as well be soon and try to hold your money together on your current car. I would guess you'd do pretty well selling the car privately with that low of miles compared to what a dealer will try to do to you.
Yeah, it's either trade it off now or wait two years. We'll probably gain back $4000 or so more than what we owe at this point. We want a long term, 100,000 mile + car (this could last us to retirement at the rate we're driving it) but just don't care for this one.