This depends a bit from where you buy a W210 (but not much) they are considered to be pretty bad rust buckets. This isn't to say that they are all rust buckets but you need to be careful when buying one.
Mercedes-Benz E-Class W210 1995 - Car Review | Honest John
Apparently the models after 2006 are better for the W211
Mercedes-Benz E-Class W211 2002 - Car Review | Honest John
I don't think that compared with the W123 or W124 there'll be as many W210s or W211s on the road in the future => meaning today I think that there are more 20 - 35 year old Mercedes on the road than there will be of a similar age group in the future when the W210 gets to be 30 years old...