The collapse of the U.S. dollar may be good news for the American auto industry and even a chance to capture some long-gone luxury-car business.

That’s because the dollar’s weakness makes imports more expensive and encourages foreign OEMs to build more plants here.

Meanwhile, North America remains a big, lucrative market, and foreign auto makers continue to expand local production.

Toyota and Honda already are well established here, and this is where most of their profits come from. The U.S. also is the most important market for most foreign luxury brands outside their home markets (although China is gaining fast).

How many more new plants could the weak dollar lead to?

Expansions are under way now. Toyota is building a new plant in Mississippi. Honda is building a car plant in Indiana (plus a jet aircraft and separate jet engine plant in North Carolina). BMW is expanding its facility in South Carolina, plus Kia has a plant going up in Georgia.

But most of these moves were planned before the weak dollar changed the game. Within the next five years, Toyota might add two more plants here, and Honda could add another, too.

Volkswagen or Audi could benefit by building more vehicles here (VW already has a big factory in Mexico).

All told, it would be easy to see another million vehicles being built here, on top of the plants and expansions we know about.

Another positive aspect is Detroit auto makers don’t stand to get hurt much by the dollar’s slide.

General Motors does import Korean cars badged as the Chevy Aveo. It also is bringing in the Pontiac G8 sedan from Australia and the new Saturn Astra from Belgium.

But the volumes on the Aveo and G8 aren’t that high. And if the Astra takes off, GM can shift production here easily enough.

“Here” means North America, including Canada and Mexico. But Canada has lost luster as its dollar has reached parity with ours, and Mexico has logistical issues and other problems.

The falling dollar presents a special opportunity in the luxury segment. Outside of cross/utility vehicles, most luxury models sold in the U.S. by BMW, Mercedes and Lexus are imported.

And European car makers are in a bind because the soaring euro is pushing their prices up, while at the same time they are being pressured to hold the line as the dollar shrinks and sales soften in the U.S.

This makes them vulnerable. Cadillac and Lincoln aren’t in the best positions to attack right now. The Cadillac CTS is strong, but something more sophisticated than the STS is needed to compete with the Mercedes E-Class and BMW 5-Series.

A new rear-drive Cadillac sedan is due in a few years, but that doesn’t help now. Lincoln has pushed into the low end of the market with variations of its Ford vehicles, and there is a new middle luxury car coming, the MKS, but it’s a front-drive design and still a big question mark.

Even so, for the first time in years price and cost issues are making the foreign luxury brands vulnerable. It would be a shame if Detroit lets this opportunity slip away.

Jerry Flint is a columnist for, and former senior editor of, Forbes magazine.