I sure could use a 4 dr sedan as my DD. Serves the family more than my Audi TT (currently getting it's 60K service @ timing belt). If I were in a position to drop the $$ I'd give your MBz a hard look.
Why not get a tow hitch on the MPV and use a light duty trailer for the bulky items? I think you're making a mistake pulling the trigger for the reason you list but I admit I have made the same mistake several times myself.
