If you buy the new, probably not. You might have a chance with the used. Sure, you'll still be able to trade either in for the Z, but will you have the equity/debt that they'll be looking for to get you a fair price on the Z? Plus, you're assuming this is when the car is coming out, could be later or sooner. If you wait, your cars value will depreciate even more so you wont get as much for it... BUT you could have a bigger chunk for a down payment. Personally if I were THAT much into the Z/28 I'd wait.
I'm not though, so I didn't.