Mileage as an issue doesn't really bother me. As you can see with the mileage on the cars I've owned, I put a lot of mileage on them. Instead of buying new cars every 3-5 years and taking a huge hit on depreciation, I just drive my cars and fix them up as I go. Any used car is going to need maintenance and repairs.
Buying a car is is not just a logical purchase, it is also an emtional one. I really like the body cladding changes on the 91 and newer W124's. That alone would be enough for me to upgrade to a newer one. The newer ones also got the wood trim on the doors and dash.
I would think the 2.6 liter might be a little underpowered for a car this heavy, and would probably want to upgrade to at least a 3.0 liter, or at best, a 3.2 in the 93 300E / 94-95 E320.
If you are happy with a 2.8 liter engine, and feel comfortable that the car is in great shape, well maintained, etc., it wouldn't stop me from trading up.
Just my .02 cents.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".