Better mileage equates to longer drive distance on a tankful. That is what I like most. Makes stops and logistic planning easier. Driving the Alaska Highway where they say to drive always in the top half of your tank was never a problem with an over 200 mile range.
Diesel inherently gives you 25-30% more energy at a 7% premium (currently where I live).
Driving mountains is definitely an advantage over most gassers. Don't know anything about the Ford Ecoboost engine that is suppose to be an equalizer in that regard other than mileage will not be as good as reported by some. That and it is not available yet in a B. Mountain driving doesn't affect the mileage in my experience. I've got some of my best numbers in Colorado and wonder if that is not more to do with the blend.
Diesel on the highway is no problem. In the city neighborhoods more service stations don't have it. Diesel is usually limited to end pumps or off to the side. Diesel is dirty in handling pumps. That all kind of adds up to a pain in the ass. And of course, gas is everywhere at every pump.
Bs are coming out with diesel powered heating and instant always on hot water. They are also substituting second alternators to charge batteries in lieu of a separate generator. This all adds up to eliminating a propane generator and propane systems and tank.
Service intervals on Sprinters are now up to 15,000 miles. They are more expensive as they recommend synthetic oil and lots of it. But I can get up to Alaska and back or just about any other extended trip without having to seek out service on the road.
Not a concern of mine but maybe a concern for someone buying a used B: Mercedes Benz says 90% of Sprinter diesel engines can expect to be on the road after 260,000 miles. I got to about 170,000 miles with a Toyota Corolla but that was about it for all the used cars I've owned. My well taken care of Subaru Baja right now needs major work at 94,000 miles. I've never trusted gas engines beyond 100,000 miles to do any long distance traveling.
I'm not married to diesel. That was simply what the engine was for the kind of B design I liked best. The engine played no part in my decision. The three service stations nearest my house I used frequently for gas had diesel so I naively thought nothing of it. In fact it was kind of a bonus because back in 2006 when I bought my first B diesel was always less expensive than regular gas. It could happen again.