I got my A4 inspected "tip to tail" by an independent audi/porsche mechanic for $150 2 months before it went off warranty. I gave the report to the audi dealer and told him I wanted everything oin the list checked and repaired in neccessary. I picked up the car and got a 5 page report of the repairs they had performed, including head gasket!!!
They must have done a few thousands dollars worth of work.
After that I considered an extended warranty but found it too expensive and had too many exclusions (wear & tear). If the car is fundementaly sound and has a good service history, I wouldn't take the ex-warranty. Its essentisally a bet that you think the parts covered will break/wear out and Audi is willing to take the bet (and your money) that they wont't break/wear out. It basically a numbers game. I think Audi is willing to accept this bet because they know that (on average) their cars don't break down.