I guess I'm of a diferent mind set. Having been in a high HP V6, after driving it for a few years, I found it lacking. So when I went shopping for a new car, I was looking for something different. When I found the R Spec and drove it, I was hooked.
As for your total cost per year, I think it's a bit off. Tires, in either 18" or 19" are about the same. And they seem to last about the same weather in a V6 or a V8.
Winter tires do not come in to play for me.
As for gas milage, I think you are a bit off in that as well. Unless your babying the V6 while the V8 guys are leadfooting it.
Insurance is probably the bigger difference, only because of the R Spec designation. I think if you just had the non RSpec 5.0, it would be closer.
But the fun of driving the R Spec in a spirited manner, at least for me, is worth the extra cost.