Luxury is a loose term when it comes to the auto industry, so for the purpose of this post, I’ll clarify that I’m not talking about the Bugatti Veyron or the latest Aston Martin. This is about Lexus, Mercedes – cars that are attainable by the average affluent Joe in the U.S.

While the auto industry on the whole has had double digit gains year on year, the luxury car industry hasn’t had the same kinds of gains (with BMW being the hugest exception, due to large sales increases in China and a more moderate boost here in the U.S.).

Cars are simply not on the holiday wish lists of the affluent, despite the fact that luxury spending on the whole was way up in the third quarter of 2012. Unity Marketing’s latest consumer confidence survey showed significant boosts on confidence and spending in Q3, particularly in the clothing, kitchenware, beauty, and dining categories. But cars remain an uncertainty.

Are the affluent getting smart and only paying for value? It certainly seems that way. Back in August, CNBC showed the top 10 most popular autos in America’s most affluent zip codes, and while there were plenty of BMW and Mercedes models in the mix, they were right next to the Camry, the Accord, and the Jetta (yes, really).

If affluent car consumers are buying down, luxury car brands and mass brands with luxury models have to fight even harder to get their piece of the pie.

That means walking the fine line of offering enough value to attract affluent consumers looking for high performance at bargain prices without diluting the brand – a feat that BMW and Mercedes seem to be accomplishing as they duke it out for the top luxury slot in the U.S.

This is not something that auto manufacturers (and certainly not auto dealers) can do only with marketing. It is not a matter of saying you offer value. It requires a deep look at price points, performance, and fuel economy – and a well-orchestrated effort to find the perfect combination of the three for affluent consumers who desire it.

It takes time. And research. And investment.

But the luxury auto brand who does it best will come out way ahead of the competition. When the pie’s not getting any bigger, how can you afford not to?