A new Mustang design has more of an effect on Mustang sales the introduction of a new model from a competeng brand. Mustang sales for 2004 dropped off dramatically after the reveal of the 2005 model. I don't think the re-introduction of the Challenger and Camaro will have much impact on Mustang sales. Other economic factors may also come into play (ie:fuel prices) that will affect all pony/muscle cars. Next year is going to be a very cool year for all muscle car fanatics!!!