I just picked up a 2011 E350 4matic. It is not a wagon. Having only owned it for a week, I'm afraid I can't be of much help. I bought the car CPO. It was the second car I have bought from MB as a CPO, and I have been very pleased with their program (previous was a 06 E350).
The cabin fit and finish is excellent as one might expect. My car has a 'performance' package, and it definitely stiffens things up as compared to a normal E class. The COMMAND system (their nav/radio system) seems to get mixed reviews as some find it confusing. I think its easy to use and well thought out, but I'm a network engineer, so make of that what you will.
The 11 model has the previous generation 3.5. I find it to be more than adequate power, but I have admittedly not driven it up a mountain pass with 4 people in the car crammed with luggage. The brakes are excellent, much better modulation than the previous generation.
Sorry I can't be of more help. The 11 models are a steal at the moment because they're now previous generation, and there are tons coming off lease.
Gratuitous photo:
