Dieselman,
I had the same concerns about the 210-606. Was very happy with my '87 300D but needed added safety of airbags for passenger. Looked awhile and found a local well maintained, high milage '97 with every option at a good price last summer. Still have the 124 because I'm not absolutely convinced the '97 is the one.
Have replaced fuel lines in the newer vehicle, and EGR and CCV mods while was there. Found the 606 engine as easy as 603 to work on. Still have to re-remove intake manifold to replace shutoff valve on injection pump, to stop check engine light alert related to fuel temperature sender malfuntion.
The 210 body is much more plush and comfortable, with heated orthopedic seats, etc, etc. The 606 engine is almost as powerful and maybe more fuel miserly.
It's a tough call and I still have two MB diesels.