Hi Simon and welcome.
Sounds like an eye watering experience you've had so far. I don't think your stupid though. You have one hell of a machine on your hands. As with all old cars running costs with wear and tear can be extreme and this will be higher with high performance motors. Running an Audi is expensive, old or new, in one way or another. Lucky you found a local garage that's able and trustworthy.
So what are you getting for the money? You have a rare 3.2 model, the car has desirability, it is putting a smile on your face when it works and the parts replaced will last for years. The drawback here sounds like the car has been used but isn't that what a car is for?
Funny enough I've got one eye on a 3.2 myself though tax and insurance is an issue for me.