Good things come to those who wait.
Don't buy until you can get the car you want, unless you have lots of money. In which case, you should not have to worry about a trade in. Just buy two.
With the higher gas mileage requirements Congress just passed, it will make it more difficult (again) for GM to produce high horsepower cars. Electronic engine management vastly improves mileage, but still unlikely a Z28 would be 34 MPG.