Normally, it's a dealer asking how to price the car, just trying to make sure profit is maximized.
For most of is here, we only would want to know what the car is worth before we dump thousands and thousands into them in repairs. If the car will never be worth $15,000, why spend $15,000 on repairs? Right?
But for many many of is, we own the cars for enjoyment, whether it's because we love driving them or restoring them, and value is irrelevant. Those are the people many of us like to have around here the most, especially when they provide lots and lots of information for all to share.
Prices change with the year, month, day, etc. All that matters with a price is that you find someone to pay what you are willing to sell it for. It could be $500, or it could be $15,000, rarely is it ever more for any 280sl. The four speed of the late 70's is a fun one to drive, but it lacks overdrive, and with a ~3.6 differential, you are really winding it up on the highway. So 4-speeds aren't nearly as sought after as 5-speeds, but actually faster than a lot of the 5-speeds and a little more fun to drive at the lower speeds. That's my experience anyway.