You have to keep in mind the W123 was designed in the 1960's and went into production in the 1970's. At the time, it was a fantastic car, despite being underpowered. And when the W124's cost significantly more, the W123 still made some sense. But it's 2012 now. W124's are available for under $2k as fixxer-uppers and $5-$7k will get you a pristine one. With ABS, dual airbags, tons of power (compared to the W123), enormously more competent chassis, and overall refinement. Not to mention optional traction control, heated/orthopedic seats, better fuel economy, etc, etc. And, they are not that much more complicated, despite what some people may think. It used to be that 124 parts were hard to come by via salvage yards, but not any more... and new parts are no more costly than they are for the 123.
I owned a 240D four-speed manual, and two W123 300D Turbos. They were decent cars but they're quicky becoming dinosaurs. The red one in the eBay listing is beautiful, but more of a collector's item, IMO. For a daily driver, the W124 makes far more sense. Almost all of the 123's flaws were corrected in the 124, and few new flaws appeared. It was a win-win. I now own a half-dozen or so 124's. All I can figure is that most 123 owners have never driven a good 124, and/or they don't want to admit the 124 is as good as it is.
For the record, I think a W123 is an ideal car for a new teenage driver. Safe, cheap, and slow enough to help keep a newbie driver out of trouble. But when they grow up, they'll want to upgrade to a W124 (or probably any other MB from the 1990's).
If you've never driven a W124, try to find a clean 1994-95 model and take it for a long test drive. Preferably a really clean example, not a beater. Just watch out of the 500E's, they're highly addictive!
