The only reason I hesitated to replace my thermostat was my unfamiliarity with this car. I understand that the operating temp is important; I just didn't know if MB thermo gauges might read low. The car was running great, plenty of warm air from the heater. But the gauge consistently read in the 65-70 range. Assuming the gauge is accurate, that is too cold for optimum engine perfomance, and could lead to extra wear.
With the new thermostat my car warms up more quickly, and the gauge reads right at 80 whether I'm on the freeway or in town. As I said before, the replacement was a really miserable job. But I'm glad that it's done, I'm sure that the engine will be "happier" running at the correct temp. I just hope I never have to replace it again!