I would not be scared of high mileage Mercs as long as they have been serviced properly .
My 430K W124 with full MBSH drove like a new car and never needed anything beyond routine servicing , tyres etc in the 20K I covered before it was written off .
I have had a W114 up to 270K , most of that mileage in my hands , again with just routine stuff ( it was manual and the clutch was replaced twice ) the car still ran well but was rotten underneath .
My current W126 was bought with 158K and has now covered over 40K in the last three years without missing a beat , I covered over 20K in the year before last , a bit less in my first year of ownership and only about 6K this year , using it less due to the increased price of petrol - currently converting to LPG for this reason .
I would not expect a well cared for 211 to give any major problems if it has been running reliably so far .
If you need to cover against downtime , a 190E or W124 bought for buttons would make a good backup car without costing the earth .