Phil,
I currently have a (W210) Jan 2003 reg E Class Auto Diesel Elegance Estate which I have had since July 2003. It has covered 198,000 miles and always returns in excess of 50 mpg on long heavily laden trips between Wirral and Spain.
It has a full service history and has had autobox oil changed every 50,000 miles. Tyres (Michelin Premacy) last at least 50,000 miles.
You will be looking at the W211 model and you should not buy one prior to 2007, when the early model problems should have been sorted. Do not buy unless it has a full service history and find your self a good Indie to look after it for you. After that join one of the Mercedes Benz Owners Forums.
Think seriously as to whether the Lexus has to go as it really does not cost much for me to keep the Merc !
Importantly for me, I can carry 4 passengers and 4 sets of golf clubs....and not many vehicles can do that.
Hope this helps and Best of luck
Regards
John
Google Mercland Nuneaton. A well respected retailer of Mercs.
Regards
John