I also intent to drive it for another 100K or so and would like both more power and reliability of a newer engine. It goes to some places that are very far from MB mechanics.
The more modifications/changes you make to the original car, the more potential there is for problems. If you want reliability stick with the basic power train. Generally speaking, with more power and faster speeds you'll get more breakdowns. Not good if you are not close to good service shops.