Some people are just afraid of change. It doesn't matter how crappy what they currently have is, or how much better a new offering is, if it's different then they don't want it.
I've never understood this mentality myself, but I still occasionally still see men with mullets, so I know that some people are just that way.
To me, the way a car performs always comes first. Any improvement in general performance makes the car better in my opinion. I'll happily take an awesome performing car with bland looks over a lot of bling with no substance any day. If the next-gen Mustang looks a bit like an Aston Martin, that's fine with me, as long as the performance is there.
What I don't want is for the next-gen Mustang to continue to handle like a pickup truck just because a tiny percentage of "purists" don't like change.