The gotcha in the clunker program was the fact that if you got a $4500 rebate for your vehicle from the gov, it is considered income for you and you have pay to income tax on it, like about 30% one financial writer wrote. Also before the clunker deal the very same new vehicle was probably setting on someone's car lot discounted 4000 or so dollars as it was difficult to move it. The clunker program might work for you if you were able to get the rebate and a dealer reduction on top of the rebate then you might have come out ok, even with paying the income tax.
I remember the good ole days when you were able to deduct the interest on your car payments from your income. Not sure when that stopped. Now that kind of program would make some sense!
Larry