I would say the OP will probably end up getting a new 09 if they do decide to get a CX-9. Unless you are paying cash, financing terms on new is definitely better. In the long run, you are probably looking at savings of a couple thousands if financed for 4 years or so.
Unless you can snag a used 07 GT for $15-$18k or a used 08 GT for $20-$23k.
Even if the price of a used 08 is say $3k more than 07, when come time to sell, you are not going to loose all that $3k. So, maybe a grand or so difference. Drive it for 5 years, it's not going to matter much.
With 2010 just less than 6 months away, an 07 would seem like a really old car by then.