With the greatest amount of respect, everything you have written there is complete horses**t.
Just because a car has been maintained at a dealer does not mean it is better looked after. Hell, I'd say it was maintained on average at a lower level. Cars like a 350z which are maintained at an independent are done so by people who care about their cars and know who to use independently to look after their cars.
The average franchise dealer YTS kid who is working on your 350z know feck all about your car.