Well...Geo... just to bring you up-to-21st century... the current headlight tech uses housing that are not airtight - so light inner condensation is not uncommon at all..the mirror water is a example of a dealership who has their pressure washer turned too high... I understand you are entitled to your opinion - but it's a opinion..
My opinion is not based on just the condensation in the headlights. I have not experienced that with my 2015 C300 may be because I dont take it to a commercial carwash. I hand wash myself.
I own a 1999 C280 with over 198K miles and a 2015 C300 with 11K miles. The C300 is fast, but loud. It has excessive road and wind noise, and MB has gone overboard with electronics. The choice of tires and suspension is very poor. With three people in the back seat, the car bottoms out even on a small bump. It is by no imagination a luxury car. Even in Comfort mode, it shifts at high reves and the ride is not smooth at all. My 1999 C280 even with almost 200K miles on it, drives much smoother, is quieterm and much better turning radius.
I think the C300 was a big goof by MB.