Like most cars, the value of this depends on the condition. They are nice, big cars and should be run on the freeway mostly. Mine got reasonable gas mileage, (~20mpg), on long trips at high speed. At 80mph, there was still plenty of power in reserve to pass or go up big hills.
It is a very big car, the size of a Suburban so it can be hard to park or manage in the city. You feel that you can never be hurt in an accident with the 560. It has a lot of complicated features such as the self-levelling rear suspension. The engine has a problem with the timing chain guide rails after they get old. Search for the link here, but know that they must be replaced or they will break and destroy the engine.
If circumstances were different, I might have kept mine, but the cost of operation was too high since I do little freeway driving now.