There's more to the car than the engine. Do you like creature comforts, like heated leather seats, memory reclining seats, a great sound system, a car that holds the road, and the knowledge that you will win an any accident.
The S Class is the finest car in the world. But, please remember that a car that originally sold for $60,000, ten years ago will not be any cheaper to maintain than a Toyota from 10 years ago - but a he** of a lot more fun to drive.
Here's my word of advise:
There is nothing more expense than a cheap Mercedes.
I personally moved from a 1993 500SEL (w140) to a 1995 E420 (w124) because the creature comforts were just getting to much to fix (the seats tore, the window regulators broke, the vacuum systems failed- both, the radio died, and the rear shocks needed replaced) but the car was a joy to drive.
Yes, the E420 can break also, but has not and has been easier to fix. BTW the M119 engine (4.2 liter V8) is great.
Please see:
http://www.peachparts.com/shopforum/showthread.php?t=236683&highlight=w124+money+pit