I'm only under water on my car if I trade it. Since I save almost all of the sales tax, it negates most of the loss of trading it and all of the headache of selling it myself. I do well financially and live modestly (the selling price of the house I just bought is less than my annual income).
I am a car nut who has owned lots of nice cars (my trade is a 451 hp German sedan). I originally toyed with a change of car to save money (gas, insurance and/or payment). I didn't expect to be as underwhelmed by the interior of the TE given the price and the great exterior. So once I was in buying mode, I expanded my search to similar vehicles in the same price range with similar capabilities (the CPO GX).