Deepening rivalries test German luxury car dominance

* BMW, Audi and Mercedes facing new luxury challengers

* Brand exclusivity undermined by sales race -analysts

* Investment returns in decline from historic highs

By Laurence Frost and Andreas Cremer

PARIS/BERLIN, Aug 24 (Reuters) - Berlin-based PR executive Herbert Franz should be a soft target for German luxury automakers - his last car was a BMW X3 - but he can't wait to leave them behind.

"This car is hip," said Franz, 52, at the city's biggest Jaguar Land Rover showroom, while eyeing up a British-built Evoque SUV that he fully intended to purchase.

Decked out in bright red blazer and canary yellow trousers, Franz might not be the typical customer in Germany's conservative premium market. But his shifting taste in cars foreshadows less comfortable times ahead for global leader BMW, as well as Audi and Mercedes-Benz.

The German premiums have long been on a roll, producing an export-driven sales explosion and huge returns while mass carmakers struggled through Europe's crisis.

But in a headlong sales race, second-placed Audi and runner-up Mercedes have both vowed to depose BMW, giving rise to heavy discounting, which sullies luxury brands and creates opportunities for the growing competition, observers say.

Now a host of younger or revived premium marques are poised to follow JLR by pitching dozens of new models against the big three, whose very ubiquity is taking the shine off their prestige.

"The German premiums have sacrificed some of their exclusivity by entering smaller, volume segments like compacts," said Bernd Hoennighausen, an automotive consultant.

"They've pushed volume with fleet discounts of around 20 percent," said Hoennighausen, who previously managed corporate fleets for Deutsche Bank and BNP Paribas.

"This may open the door to newer players like Jaguar, who are starting to offer fleet-relevant products."

Among others waging or planning new offensives are Fiat-owned Maserati and Alfa Romeo, Nissan's Infiniti, and Volvo, a unit of China-based Geely.

"Our theory is that there's room for something visibly different that is styled in a more provocative manner," said Andy Palmer, the senior Nissan executive charged with achieving a breakthrough for the 25-year-old Infiniti brand.

"It's particularly true for China," Palmer told Reuters. "Chinese consumers will cross-shop - and Audi only has the market to lose because they've been so dominant."

For now, the Germans remain firmly on top. Their combined sales amounted to 4.7 million vehicles last year, almost 60 percent of the global luxury car market, according to consulting firm IHS Automotive.