I think there are a few issues that Mercedes should address to get things moving:
1. There are major markets that have no Metris or Sprinter dealers. Minneapolis for one.
2. MB should make some things available. Options like the Viano upscale van, 4-Matic and diesel.
I don't understand why MB doesn't exploit thier unique position in the USA marketplace. These things exist in other markets. It's like they are wading slowly in the lake rather than going for it.
Actually, i think you are thinking in the wrong direction. The Eurovan never sold in big numbers either, and was discontinued. The result is that 15 year old Eurovans are worth insane sums for their age and mileage. There will always be a few people who would be willing to pay good money for a very fast transporter.