Read some of the comments on news stories about the Metris and the reason MB doesn't import rapidly is obvious. I have owned Mercedes cars for years, some of them very Spartan. I know what first and foremost Mercedes means- quality, durability, safety, and engineering excellence.
My 240Ds and to some extent my other E-classes were basically taxi spec. The idea of a van from the same manufacturer is not incongruous to me. Mercedes vans are not luxury products- In fact a diesel Ford Transit, by some idiot mistake on Fords part, is slightly more expensive than a comparably sized Sprinter.
You generally pay a bit more for a Mercedes, sure, as you do in every segment they compete in.
Mercedes is having a hard time convincing average buyers that their cars are not much more than competitors, and worth the premium. The publics perception, because they don't know MSRPs is that a FedEx Sprinter is a $80k truck, not the ~$40k or so Fedex actually pays for them.
They have to move carefully to both properly build their commercial identity, and not hurt their luxury exclusivity perception for their car brand.