The warranty is really up to you - Audi Pure Care is underwritten by Fidelity, perhaps the biggest, oldest and best of these providers - it is managed by the servicing dealer- usually looks and feels just like the Audi factory warranty for the most part - and overlaps with it. That means, if you have Pure Care on the car at the same time as your factory warranty, only one of them will pay - and the Pure Care terms START at the same time as your factory warranty - NOT after it runs out. So a 6 year Pure Care is for a TOTAL of 6 years, NOT the factory 4 plus 6 for a total of 10.
Based on your comment of mileage, it would depend upon the term. If you're the type that needs a new car every 2 years or so, forget it, unless you put 30K a year. But if you only put 10K on it and you expect to have the car after 4 years, I might consider it. Same with Pure Protection - it's a pretty good deal for high flyers, but prolly not so for low miles over a longer term use...