I was all set to buy a Ford chassis and in my final round of research I test drove an MBS right after driving a rented Ford Sunseeker for a few days. The difference was night and day. The MBS was quieter, had smoother power, handled far better, and had much more room in the cockpit. The fact that it gets better gas mileage and looks sharper were extras for me.
I've been on the road with my new MBS for two weeks now, and I couldn't be happier. It drives so comfortably that I feel like I can go all day, and when I need to I can parallel park it in town pretty easily. For me, those are the reasons to get an MBS.
I think I paid about $13k extra for it through an online dealer compared to a comparable Ford. To me, it feels totally worth it.