While there is still a good market for this type of car and there will probably always be a demand for it this is a totally different sales environment than it was in the 60s, 70s and even into the early 2000s and I think my previous statement still does apply. Times change but I think a lot of people don't want to change with it.
You may want to double check your thoughts on sales numbers.
Mustang sales stayed pretty consistent in the ~120,000-~150,000 range for all but a few years between the early 1980s until the late 2000s. From 2008 on is the first time yearly sales have stayed well below 100,000 for an extended period of time. That also happened to be the time that the economy tanked as well as the reintroduction of the Challenger and Camaro.
As much as I think the 2010-2014 is the best looking Mustang Ford has put out in a very long time I can't deny that it's time for something different.
You also have to factor in price and the market. Back then, the Mustang was much cheaper but then again, it was also not as well put together as the newer cars are today. I think the Mustang will do okay, but it's no longer a 22K bargain like it used to be for a GT.
2012 Mustang GT Premium
BLACK on BLACK 401A. A6, HIDs, Security, Rear Camera+Reverse Sensing, Remote Start, Comfort.
(Planning on CAI/Tune then I'll be good)