I bought a 2008 Cobalt at 77,000 miles in the summer of 2011. Just rolled over 100,000 miles. Had a few common problems. Transmission had to be rebuilt under GM Powertrain, both front speakers failed, lower control arms. This is all things I would expect with a disposable GM vehicle. I noticed in the snow that maintaining a proper alignment was key to driving straight, and adjusting the rear brakes was key to stopping. The paint still looks brand new even after $4,000 of paintless dent removal. The car has always been dependable and I don't plan to trade mine in.
The Higher ratio 5-speed transmission helps me get about 36mpg if I try, and 32mpg if I beat on the car for a week. I like that Chevy still offered this car without options to keep cost down. I was ably to find one without power windows, locks, or an automatic, but could still get the SS spoiler, and Wheels. I praise the balance shafts in the engine. I never had a car i couldn't tell was running.
The transmission needsto be a higher quality. The engine need stronger crank/pistons/rods/and rings. You can't modify the car too much without burning up the motor. I would delete the solid rear axle.