The 450SEL featured a hydropneumatic self-leveling suspension.
The engine in this car was a V8 with sodium-filled valves that are usually only found in piston aircraft. This engine could take a beating for a very long period of time. Each one was tested for hours on end, often at full throttle.
Because the engine used a dry sump system, it only needed an oil change about once every 12,000 miles. Other elements of this engine also made it very easy to maintain. This engine could go for 50,000 with little more than a few oil changes. Find me another car that can claim that.
This car retailed for between $40,000 and $50,000 depending on options. They have not maintained that value, and now are worth about half of their new price. Look for them to gain value in the future with collectors.
Try finding these cars on eBay, especially the 6.9. They are primed to go up in price as collectors realize how far ahead of their time they really were.