I can't say that I have ever noticed the difference in service in ET/CE depending on fare type, but I have never actually booked a full reward ticket in CW or above before.

I've noticed a slight difference in offering on occasion when I have received the odd op-up. It is usually in the form of no breakfast offering apart from tea, coffee,or croissant and the absence of a CW amenity kit. Being upgraded free gratis is a fabulous experience I have to say, and was always informed of the slightly reduced service from the outset...I've been well happy with these situations!!

Generally speaking I would suggest something similar to the nocebo effect coming into play here