Been awhile on this topic, but I can give some insight. We bought an 06 Hemi Adventurer new in 06. Just traded it in on a 2013 Hemi Crew. Put 140000 miles on it including some hard towing. (Imagine a 21' dual axle car hauler with a 1997 F150 4x4 extended cab on it behind the D. The trailer combo was probably double the weight of the D.) I was meticulous at changing the oil and used nothing but Amsoil 5W20. The only things that failed on it were the EGR valve at about 40k and the transmission controller solenoid pack at about 110k. I changed them both myself. We had no issues with the motor or trans other than that and it was still running fine when we traded it.
All that said, I do have a friend who purchased an 06 Magnum with 50k on it. At about 80k he had to have the entire upper end replaced because the MDS crashed. Those are two data points.
I'd say if it's been maintained well, there would be no problems.
Economy wise, I have an 04 D2500 with the hemi without MDS and it gets about 17mpg. The D with MDS gets about 18.5 if driven in a similar manner for waht it's worth.
