I've had one for close to 10 years with no issues at all. At one time Kimbers's higher end guns used an external extractor. While an external extractor done right is just fine, these appear to be the versions that gave Kimber a bad rap. I have never heard any complaints about their base model Custom II that always came with an internal extractor.
Is it worth $800 used? I don't know for sure. But I do think you will like the gun if you can get it at a fair price.