Well, that's interesting views on purchasing a cat d car. Personally if I was buying a car for keeps (at least 3 years), that would not put me off especially if it had all the extras ; the colour was right and mileage was good. This is providing the owner has pictures of the accident which made it a cat d and any other documentation. You have got to remember with part & labour prices these days it is quite easy to write off a car. In fact it's probably not uncommon to have a number of cat-d notices on a car especially on the earlier A/S3s ! Your going to check the suspention and body and so you will have a pretty good idea if the car has been repaired well - whoever who has done the repair. If anything here's an opportuntity to purchase a car for exceptional good value as your bound to negotiate some reduction in the price.
If it has only recently been repaired from a cat-d and put up for sale then I would be worried quite a bit more !