I have encountered several problems in my A8 over 2 years of ownership. I have water coming inside the car by the footwells.
It turned out that the airconditioner drains were plugged. They did get cleaned out and the water problem disappeared.
After that it seems just for fun my signallights, wipers, lights would fail to work out of the blue.
If I shut of the engine and restart it all is back to normal. The light for the abs sensor comes on whenever it feels like.
It was tested by my mechanic and it showed that 3 sensors were faulty (highly unlikely). Also the fan for the climate control would by itself go up or down in speed when it was set for the highest speed.
Could the wiring have been affected by the water problem from the plugged drains?
I love the cars but am getting sick and tired of being an unofficial Audi sponsor.

 

Wlcome to the *joys* of Audi ownership. I haven't heard of anybody equating those kinds of problems with the water from the plugged drain holes, but, I haven't heard it all, yet! I have heard of random instances of the kinds of random problems you've described, as well as some I've heard of and experienced that you haven't mentioned, YET. I won't say what they are 'cause I don't wanna ruin teh SURPRISE - LoL.

it seems that, in order to be technologically advanced, in the quattro department, Audi sold it's (electrical) soul to the Devil

 

IMHO those are definitely not related, but both issues by themselves arent exactly uncommon. Speed sensors I'm unsure about, a number of people with A8s, including myself, have the ABS light come on with the code for those sensors, but then they seem to disappear once again.