Not speculating about future or past values, taking a snapshot of the deal you are considering doing today, it is a square deal.
Sounds like you are getting a discount on the 09 and a good trade on your 02.
Gen V Viper will not be available to general public for about a year, so that is not in the discussion for a deal being done today.
The Gen IV ACR is the current king of the hill (and the ring). It has street and track performance capabilities far and away from your bumble bee (term of endearment for yellow/black) It is faster, quicker, better handling, spectacular looking, better mileage, smoother driving, better A/C, better brakes, better driveline, superior quality of assembly and parts.
People go nuts over this car. It has rock star status.
If you take it for a ride, you will want to take out your checkbook.
Most of the left over Vipers at dealerships are pretty picked over, with few popular colors.
Best of luck with your decision. Either way, you still get to drive a Viper.
Please check out the VOI information on this site. It is a huge party, thrown by the Viper Club of America to enhance the Viper Ownership Experience.