I'm not sure that rain sensing wipers were available prior to the face lift.

Rest mode only works with heat - there's gobs of hot water available in the block to keep he heater cores warm - not so with freon.

Outside mirrors are heated electrically, and are sadly tied to a thermostat. They don't come on unless it's below a certain temp. I'm pretty sure they're in the same circuit as the electrically heated windshield washer nozzles, which come on below 41f and cut off at 59f. On previous cars I've owned, the heated mirrors were tied to the rear window defogger, which on misty mornings works really well to clear the mirrors.

The windshield washer fluid is also heated, but by a heat exchanger coil in the tank (which is up inside the front bumper on the passenger's side) which passes engine coolant through the tube. This also has a thermostat on it - also opens about 40f. Many people confuse this tank as being an alternate overflow for the radiator, since they see radiator hoses going into it.

The PSE pump under the passenger rear seat cushion does a lot of work for these cars:
Lock/unlock doors/trunk/gas cap.
Extend/retract trunk handle.
Assist trunk closing system by extending the retracting pawl when the trunk is opened.
Extend/retract parking assist masts in corners of rear fenders.
Provide vacuum to release rear headrests when commanded from button on console.
Provide air pressure to inflate lumbar supports.
Provide assist vacuum to operate HVAC, especially in REST mode.

The system that handles the auto-close of the doors and trunk is a separate pump mounted inside the trunk on the driver's side up behind the back seat under the package shelf behind the covers. It can be very finicky about the doors, uses a time/pressure system to figure out when a door is latched, or if one of the doors has a latching failure. Repeated failures of a particular door to meet the parameters the system has outlined for a successfuly close event will result in that door being taken "off line". Visit www.v12uberalles.com for a great writeup on how to adjust the pump to virtually eliminate these off line events.

I'm pretty sure your model is sufficiently old to allow you to pull codes for the various computer controlled systems by building a simple code reader. This website has a lot of useful information on building the reader and reading codes: http://pages.prodigy.net/jforgione/MB_S500.html.

Being able to wrench on these cars ourselves makes them affordable to "mere mortals".

If you have any questions - don't hesitate to ask - that's what we're here for.