I just went through this same analysis and decided it better to buy a 2009 ACR than a 2010. Following was my thinking:
1. The 2010 is virtually the same car--slight differences, possibly worth a little, but not much. Ask yourself how much you would pay for a 2009 (with 2009 specs) versus a 2009 (with 2010 specs). $1k, maybe $2k? I can't see much more for the slight differences.
2. The 2010s are not available right now, and probably won't be for many months.
3. When the 2010s are available, because of the low production numbers (370 on all 2010 Vipers?), and no new ones coming in 2011 (at least), there will be NO reason for the dealers to discount them. Therefore, they will likely be selling for what, $10k more than the 2009s?
4. There is NO reason to believe you will be able to buy a 2010 at 0%. Depending on the rate you can get, that alone could be worth another $10k+ (in addition to the price of the car).
5. As for "future value," I don't see the 2010s as being worth significantly more than the 2009s. Last year of the model. So what? So were the 2002s for the RT-10s and GTS. So was 2006 for the Gen. IIIs. Are they worth significantly (any) more than the 2001s or 2005s? I don't see it. If you think so, I have a 2006 SRT-10 Coupe for sale right now--give me a call (816-225-6060). I'm happy to put you in a "final year" car (for the Gen. III) for only $20k more than you can buy a similar 2005 (I know they didn't make coupes in 05, but you get my point).
I could have bought either (or both), and certainly thought about waiting and buying a 2010 ACR but, in the end, I decided it made more sense to buy a 2009 ACR.
As for that car . . . I should get it tomorrow or Friday!! Can't wait!