If I had the opportunity to do things diffently, I wouldn't. So I guess that means I think my car was "worth every penny". I drove the E63, it was a fine sports sedan, but it just didn't click with me. My love affair with Audi was over before it started. I sat in the Panamera, and decided not to drive it, lest I enjoy it too much, because I personally think the car is hideously ugly. These are all personal preferences.
I have zero buyers remorse over the M5. I absolutely love driving it through the twisties, its better than any video game. And for some unexplainable reason I also find myself grinning like an idiot when driving it at 25 mph in a straight line in traffic. I used to hate going to the store for milk, now I'm looking for any reason to run an errand. I love the feel of the steering wheel, the phenomenal seats, the arrangement of the dash/instrumentation, the driving feel of the car, the sounds it makes, the way it looks, everything.
I don't know if this is the car for you, but it was definitely the car for me.