Congrats, great looking car!
I went through the same process with Ford, threatened to go through the BBB AutoLine as you did, but dealer ended up getting on them and they offered me the same buyback terms as you stated above.
I ended up ordering a 2013 Escape to replace the 2012 Focus. Overall, much better vehicle, but suffers some of the same inherent first year issues like the Focus. At least the 2.0 EcoBoost is a gem of an engine and the transmission behaves much better than the PowerShift. Most of my issues are build quality related (rattles, trim issues), sagging rear view mirrior, and the atrocious MFT system (latest is the rear view camera parking lines turning themselves off). Still the same old attitude issues when dealing with Ford CSM's, when will they learn?
I am confident you will not have these type of issues with the 2013 Mustang, it's a solid vehicle, without the Euro reliability issues and without MFT. Enjoy!