I personally would NEVER buy a a CAT-S car. If nothing else, it will be hard to sell on and the insurance will be a pain.
You said the inspection shows all structural parts to be original. A CAT-S is structural damage, so that would worry me too. The car may have been repaired fantastically, but how do you know? Also how does the next owner know?
If it is VERY cheap, then maybe worth a punt, but from what I've seen lately, cars on a CAT anything write-off are not cheap enough IMO.
HTH