What kind of mileage are you getting with the GrandAm? It can't be THAT bad, can it? Is it paid for?
You're looking at $14,000 as a trade-in on that car. $16,700 if you can sell it to a private party. If your car is paid for, you're going to have to fork out (at least) $16,000 for a new, $30,000 car. Even at the minimum rated mileage (20mpg) and gas prices at $3 gallon (worst case scenario here), that $16,000 will buy 5300 gallons of gas, taking you a whopping 106,000 miles. That's assuming you earn no interest on that money and not accounting for inflation. Given your current rate of driving (15,000 in ~1.5years), that's 10 years of driving.
Just keep your current car. Drive it till the wheels fall off, that's the most affordable way to own a car anyway.