The constant mention of RUST certainly adds to the notoriety and fear of E9s. A bit like talk of a recession causes a recession. Personally I prefer our cars thought of as enthusiast or hobby cars, it expedites maintenance and upgrades in that we are not reticent to use a non standard, and usually better, part to keep the car going. It also frees me from being an originality snob, - "mines better than yours because it's original and yours isn't so you can't be a member of my very special car club".
On the other hand I can understand the thrill of the chase in obtaining a pure object. The bar can be set very high for some. I have a 1990 Honda RC30 which is 100% original and I wouldn't dare stray from that but it also means that this bike will not be ridden for fear of degradation or damage, so it's not a motorcycle anymore, it's an artifact. The only thing not original is the air in the tires. So what happens when I do have to replace things that have perished, like fork and clutch seals? Should I keep the original replaced seals in special storage? It all gets a bit silly.
Early small bumper Porsches were just as prone to rust as E9s yet, weirdly in the strange logic of the collector mindset, one of these cars having had a full restoration including replacement of much of the bodywork, trim, mechanicals, etc is considered original as long as everything is period and model correct. Go figure. Maybe this is why there is such an interest in "patina" cars now. Even major art works undergo restoration, some quite extensively. Does that mean they are no longer a DaVincis or Michaelangelos?