Lexus has become a serious threat to the Germans in the US and has outsold them for the past consecutive six years. With sales of over 300,000 last year, Lexus has sold more cars in the premium segment than any other manufacturer.
But with this success comes ubiquity. In many markets, like Dallas, for instance, it seems every other car is a Lexus. Over time, I think this can be very detrimental to brand image and prestige.
For reasons that have been previously discussed on this forum, this phenomenon of Lexus dominating the luxury segment is strictly limited to the US market. In Europe, Canada, and Australia, Lexus is not widely known, respected or considered serious competition to the German trio.
I've already heard a number of Lexus owners (particularly women driving RX330's) say that they won't be buying another Lexus because they see so many of them.
So the answer to this question is, yes. Even though Mercedes was the sales leader in the US until 2000, they never sold 300,000+ cars. Why? Because they never seriously marketed cars that were inexpensive enough to grab the demographic that Lexus has grabbed.
So, essentially, Lexus has cheapened and diluted it's brand image by selling so many cars to the masses, and the more they do this, the more brand image will suffer.