100% I'd buy it if it had been repaired properly. And I'd expect to get it for 60% of the non-Cat price. Bargain!
It's personal choice but I don't even know where to start or how long it would take to explain why it's a sweeping assumption to assume there is anything wrong with a repaired Cat.
In short Cat C/Ds have a lot less to do with the amount of damage and it's repairability and everything to do with the finances involved in doing so. Write-off/Total loss refers to finances not physical condition. And those finances don't just cover the body shop costs. There's other overheads like courtesy cars for the insurer to think about. These categories work fine for newer cars but can be completely misleading with older cars.
Apart from a little jig work, that is a very easy repair in the grand scheme of things. People on these forums have probably bought Z3s with much more relevant major mechanical work completed, possibly to a sub-standard and of much more risk than a Cat car carries.
It's even a mis-apprehension to assume insurance companies rack their premiums up for Cats. My insurer Footman James doesn't and I believe many others don't too. Why would they? They need the revenue from selling write-offs for rebuild. So they'd be shooting themselves in the foot.