The Chad, I hope this isn't coming too late, but I was in the exact same position as you: 21K buyout on my 04 with retail value being under 18K. Then I noticed all the dealers in our area (ottawa) with heavy discounts on new 07's. I decided to give it a shot and ended up getting a 07 GT + all the same options/color for almost 15K under MSRP (mind you lots of negotiations were involved, but they started around 10K off MSRP which is still a deal).

If you love the car, can withstand the fuel cost, and don't mind a 5 year buy for the price of a 4 year lease, a real deal can be swung with the dealers right now.

Aside: I tried a Sky Redline to see if it could be a more fuel efficient alternative to the 8 (7L/100km highway @ 260hp), and while it was faster in a straight line than the 8, it can't even come close to the handling. After unfolding myself (and re-locating a few joints) getting out of the sky, I went to the Mazda dealer and didn't look back =)