I'm not considering it for its cost savings...that's why I agree that the diesel makes the best 'base' engine! Forever now, you'd have to pony up big time to save $ at the pumps while losing performance/power. It makes little sense to a consumer, causing calculations to fly.
Now, if you want the more powerful engine, you pay more and accept that it will use more gas (and you can make your own calculations). No way the diesel will cost more to operate than the 3.0T though even with the higher price of diesel fuel. If you want better performance, buy the petrol. If you are content with basic performance and decent fuel economy, diesel is your base engine. Perfect, IMO.
...but imagine a 2.1TD C-class, aka C200 with 200hp and 369lb-ft while returning combined 6.5L/100km?
...and the best part is that it's coming.