Star Specs will chunk if you overheat them, as you've found out. Once they get greasy, back off for a couple laps.
Adding negative camber will help with the wear on the outer edges of the tires, but adding too much up front on the stock suspension will result in an unpredictable handful when driving and racing. There's no way to adjust the rear camber stock. You can get some negative camber in the rear by lowering the car, which will also allow you to run more in the front and keep the handling balanced. The best option for adding negative camber in the rear are the whiteline adjustable control arms.