In the early days it was simple, win on Sunday, sell on Monday! The cars were production based. That's why it was called Stock Car racing! And there was mutual benefit to the auto makers and the racers. Manufacturers learned through racing how to improve reliability and safety. There was a true symbiotic relationship between the two.
Even later when the cars were less "stock" this relationship existed. Manufacturers used racing as a form of testing that still improved the road going versions. And of course the marketing ties were obvious. You could buy a car that looked very close to what was being raced. But what about now?
The production Ford Fusion is a great 4 door midsize sedan, with a compitent chassis and selection of powertrains. The NASCAR version is a tube chassis and composite body in the shape of a 2 door coupe. Production comes with front or all wheel drive and either 4 or 6 cylinder engines. NASCAR? Rear wheel drive, Carburated V-8. When was the last Carberator used in a production car? 1990? So, what development are we getting from NASCAR?
As for Marketing, it could be argued that the truck series is "relevant", but barely.
The V8 engines used in Production vehicls are Overhead Cam Multi Valve technical beauties.
The V8 engines used in NASCAR? Overhead Valve Pushrod engines, really nice, but not cutting edge by production standards.
So, in my opinion Ford and GM and Chrysler would be better served by cutting their NASCAR budgets out. The bang for the buck isn't there.
From what I've seen on TV they'd be better supporting professional wrestling.
Or God forbid, American Idol? Go Ford?