The big question is: Which model do you blow your one-time exemption on? A relatively new model that has also been sold in a US-spec version? Verify what it would take to convert - economics may make this impractical. A model that has never been sold in North America? If conversion to EPA/DOT specs is required, possibly impractical or impossible.
The only possibility I see would be a pre-'68 model that is in such great condition and at such a good price that it would make sense to perform a modest conversion to US specs (kilometer to speedometer change, etc.) and pay to ship it home (or as a serviceman could you ship for free/reduced price?).
It's my understanding that Germans hold older MB's/BMW's in as much regard as we hold older Cadillacs or Lincolns. In other words, an older S-Class may be cherished over here, but in Stuttgart, it may be on it's way to being run into the ground, just as we would probably run an old Park Avenue or deVille.
Search carefully for a sound candidate (pre-'68 w113 SL?) and factor in conversion costs/efforts into the equation.