This sounds similar to what Tiffany & Co. went through in the past with their line of intro level jewelry. Their target market was for those who really wanted a piece of jewelry with a Tiffany's name on it at an affordable price. They started to pump out silver jewelry priced so affordable that teenage girls were wearing and they were sharing the same prestigious and precious value of owning a Tiffany's jewelry. Not that this is wrong, but some of the "original" customers were turned off by this and some even sold their Tiffany's jewelry because they felt that their jewelry had lost its exclusivity. After learning this, Tiffany's started to increase the prices on these intro line of jewelry but its safe to assume that what they gained in additional revenue from their more affordable line of jewelry, they took a hit on their image and perceived value.
Same thing could happen with BMW. I personally don't care too much to a point where I would boycott the M brand. Obviously the M division is doing something right if everyone wants to be a part of it (even the ricers who add on a M badge on their civics). But I will be honest and admit that it does bother me just a tad bit. The M cars have always been very special in delivering exceptional performance and also provided exclusiveness to the brand.