The Charger is bloated because it's a "powerful" car for the people who have kids and aren't going to be able to get a car dedicated to power or performance.
They wish they had the Mustang, but they need 4 doors so have to settle for the Charger. Better than opting minivan or Taurus, I suppose.
(Although the Taurus SHO is a pretty mean looking car...)
I don't complain much about Z part prices. In my mere 10 minute commute every day, I will see about 10 Chargers and 8+ Mustangs all told. I'll see a 350Z maybe once a week and a 370Z maybe once a month. I like the rarity, and the part prices will have to go with it. I see a Porsche probably every 3 days.
I could also say, of the 10 Chargers and 8 Mustangs I see, they might all be optioned out differently, at least.