Disclaimer: I work for the US auto industry. Not in factory building cars. Well, sometimes in a factory, but I don’t directly build cars.
As Exapno Mapcase says, if you want to view your car as a pie chart, it really can only be done on a car by car basis. Also, all things being equal, it truly can be better for the US economy to purchase a so-called American car, regardless of its percentage of content, and even regardless of where it’s manufactured. I’ll get to that…
…but first, buy the car you like for the reasons that you want. If you’re worried about quality, GM and Ford have recently equaled (and in some surveys, bypassed) Toyota, and are just about par with Honda. When people talk about “Japanese car quality,” these two are the benchmarks. Nissan, Mitsubishi, and the others aren’t in the same leagues. The Koreans have come a long way, but still trail. The Germans still trail. Among the Americans, Chrysler still trails, but there are indications that they’re improved (not enough longer term data). So in most cases, quality isn’t a major reason for making a decision. Taste is.
The auto industry is a lot more complicated than “parts come from X,” “it’s assembled in Y,” and “the profits go to Z.” Cars take years and thousands of people before the first one rolls off the assembly line. Here’s a very abbreviated overview, and it goes for Japanese, Americans, whoever. I’m going to miss a lot of stuff.
We’ve got to identify market needs. Big team of people. Next, we’ve got to design the car. Team of people. Next we’ve got to decide to build the car. Then we’ve got to package the car – huge team of people. Next, can we build the car – big team of manufacturing experts. Clay models, which despite the term consists of huge quantities of materials and respective fabrication experts. Prototype builds, consisting of a full plant of people including skilled trades, operators, fabrication specialists. Manufacturing specialists, who design the assembly lines. Manufacturing specialists, who supervise the construction of the lines, and the launch in the plant. Vendors, who rep the people that make each component in the manufacturing plant, including sales, technical support, field service, applications engineering (several whole companies). Vendors, who rep the people that make each component in the automobile, including sales, engineering, technical support, field service, applications engineering (several whole companies). Steel suppliers, tire companies, robot companies, seat companies, light-bulb companies. We still don’t have a car, but we’ve involved several thousands of people at this point. Finally, we build the car in the factory. The plant employs 2000 hourly and 200 salaried, which is just a tiny little dent in everything that’s gone into it (and I’m skipping a heck of a lot).
Where do these activities take place? Where do all these people earn their salaries? More importantly, where do they spend their salaries? In the case of a Japanese or European transplant, the vast majority of this pre-engineering takes place in the home country or home region. Sure, a particular plant employs a couple thousand people that prop up a local economy, but it doesn’t support too much outside that region. All of the massive numbers are the behind-the-scenes work that no one ever stops to consider.
What about American plants in Mexico? Again, only the final assemblists work in those plants. All of the other work takes place in the United States. The GM plant in Silao and the Chrysler plant in Toluca and the Ford plant in Hermosillo all require the direct and continued support of employees in the United States, and suppliers in the United States. The Nissan plant in Aguascalientes requires similar support from their home base in Japan.
Is it better for the US economy to buy a US brand car? Absolutely. But… don’t compromise and buy a US brand car just because you’re guilted into it. This is a capitalist market, and if everyone were to buy American just for the hell of it, you can guarantee that we’d be back to the quality of the 1970’s and -80’s. Competition has made American cars good again.