I have had 2 E55 Kompressor cars, a sedan and now a wagon. While they are easy enough to live with and generally reliable, I can also verify they are substantially more expensive to own than a six cylinder 211 car.

The most obvious distinction is fuel economy. A 55 will typically deliver 15MPG. A sedan can maybe touch 21-22 highway, but in generall figure 15 city and 20 highway if you're driving style is not too crazy. The only other normal expense which is significantly different is tires. Figure on $1K as an average cost for a set, and a lifetime of 10K up to perhaps 30K miles at best.

In terms of potential E55 repairs, you have all your standard 211 items. Plus the E55 has airmatic suspension standard, and the air struts definately don't last forever. Rear struts cost $2k to replace at dealer parts/labor prices ($3K for the pair), fronts are a bit more reasonable. Other common issues are supercharger clutches, serpentine/supercharger belt pullies, and intercooler pumps. Some of these are a bit pricey, others not too bad, but it all adds up.

Moving on to other topics, it is my understanding that MB is fully covering the balance shaft issues these days. As well, most '08 models are out of the affected range of engine numbers.

SBC brakes were removed from all 211 models starting with the '07 model year. Lack of SBC would be a cost of ownership advantage of a newer gasoline car over an '06 CDI.

My $.02.