You won't regret it. 09-11 is this body style (c6) the 12+ body style (c7) are pretty slick too. Test drove a few different vehicles, but the c7 are still pretty expensive... The kicker to buying mine was that it only had 23k miles on it and nearly a year of warranty left. Make sure to get the supercharged 3.0, it's fun
Yes, Audi's are great. Growing up in Germany and my father being the line supervisor for the interior assembly at Audi for the 100 and then A6, we had a new one every year as the old man got great factory employee discounts.
With 23K on the clock I would agree that you have gotten yourself one awesome ride. However, I have not heard of any Audi's running trouble free like our Tahoe and Yukons with 150K plus miles on them. An Audi with 300K miles on it I have never heard of.
I had an A6 Quattro once which was an awesome car to drive, a total pain to maintain. To change the timing belt (and at that time you will change the water pump as well) will cost you 2.5K and that is not a dealer price.
You will definitely not wrench as easily on an Audi as you would on your old ride (unless of course you are a mechanic by trade and have the additional knowledge).
Congrats on your new beautiful ride and I wish you all the best, but I am willing to bet that you will sell this car before you will reach the 100k - 120k Mile mark.