Key determinants are who will keep up the car and how often will it need attention. It might be cheaper for your friend to keep up his 560 but not for someone who will take it to a shop. A 560 needs attention more frequently than a Corolla so that's a factor for someone on a tight schedule. I wouldn't think twice about going 12K miles between oil changes in a Corolla if the manufacturer recommends 10K mile intervals. I wouldn't dream of it in the SDL.

I agree with what you say. Look at the purchase premium on an E320 CDI over an E320 gasser (a couple of years ago, anyway) or the premium of a Powerstroke F-350 over a gasser F-350. The difference will probably buy enough fuel and tune-ups for the typical duration of the first owner's use of the vehicle.

Sixto ... tangents? we got tangents
95 S420
87 300SDL