...there is something to be said about having what amounts to a $6K maintenance/repair fund sitting in the "Bank" (or, "un-borrowed", as you prefer) vs. buying (or financing?) at the $11K figure.
Either car could (perish the thought!) come down with a mandatory major repair (say a tranny rebuild) sometime after the limited warranty runs out. The big difference is whether you can afford to foot the bill for the repair IN ADDITION TO the $6K extra investment in the purchase price of the 560SEL. In either case you would know for sure that the affected component had been repaired: the total co$t$ of owner$hip over the longer run must be recognized, though... $6,000.00 represents a lot of preventative maintenance and normal repair costs. Might last you quite a few years. Are you planning to keep it for long? Daily driver?
560SEL's are more complex & have more features, as has been previously mentioned. Both are wonderful cars. There is a measurable (but not IMHO "dramatic") performance difference, as well as additional costs to insure & maintain. How much risk are you willing to assume? How much routine maintenance work can you do yourself? How long to you plan to keep the car? Can you afford a major repair above and beyond the additional purchase price? If these questions are not considered prior to the purchase you will, probably
, eventually have to deal with them.
If this was a choice between two less expensive to repair cars (say two '65 Mustangs, one restored & one a low mileage original) and the difference in purchase price was still over 50%, which one would you choose? The one you could work on and update to your satisfaction or the one already done? Is it going to sit in a garage and be driven on sunny Summer days only, or be expected to reliably get you to work in all seasons?
If you had $20K to start out with, were not interested in (or inclined to) doing any work yourself, enamoured with the extra features on the 560SEL, I'd call it a toss-up! Most people with $20K available would buy an even more expensive MB to begin with.
You roll the dice anytime you buy an older vehicle: sometimes you CRAPOUT!
& sometimes you WIN BIGTIME!
Good luck with either choice!