The w211 wagon is a good all around car, but I don't really see the point of the E500 variant. The E500 has more standard equipment and is generally highly optioned. On the downside, the E500 has 4matic, airmatic, and SBC. All E500 cars have the 722.6 5 speed automatic.

There's nothing wrong with 4matic, but you hardly need AWD in Flower Mound. While it's reliable, it does cost you fuel economy and you may have to replace the front axles at some point when the CV boots give out.

Airmatic is 4 wheel air suspension. The struts don't last forever. They are very expensive to replace - about $5K to do all four corners of the car for parts & labor at dealer prices.

SBC is Sensotronic Brake Control - brake by wire. It's not as bad as it's reputation, and MB warranties it for 10 years from new. However there is some exposure to expensive repairs, particularly after that 10 year warranty expires.

An E320 wagon ('03-'05) provides all the same basic goodness, better fuel economy, comes with or without 4matic, and airmatic is very rarely found on them. It does have SBC.

An E350 wagon ('06-'09) brings in the potential of the m272 balance shaft issue. Lots of information available here and elsewhere on that. Early models could be had with RWD or AWD, but at some point ('07?), MBUSA product planners made 4matic standard. But as of the '07 model year, SBC went away, so that's one less thing to worry about.

I bought an '06 w211 wagon about 2 years ago. It's a coddled, dealer CPO car, so maybe not representative of most. So far the total repair bill is a fresh auxilliary battery. No mechanical repairs or problems of any kind, just scheduled maintenance. It's a great road trip car.