Why is it that you want a new car? Some new feature that you can't get in your old car? Reassurance of a warranty? If there's really nothing of that nature that you can't put your finger on, then I say build up the old engine. You'll be gone a while, so if you have a reputable mechanic that will do the work for you (and not sell it out from under you when you're gone) then make yourself a monster of a car. It would be especially great if you pulled up next to a 2011 Camaro SS or Mustang GT with your "old" sleeper car, and let them have a good look at the tail lights.
And I agree with Gill. Car payments blow. If you do buy new, try to pay it off in just a couple of years if you can.