I always find that photos actually make a car look about 30% better than when you see the same car in real life. Photos seem to hide all the imperfections, scratches etc. So considering this, this CS was probably very tired in the flesh, so definitely a high price paid.
I think the premium would be for a) a top 3 favorite E9 colour, b) manual transmission c) looks very original.
I noticed the auction house estimate for the E9 was just Euro 15-20K and for the 635 CSi just 5-10K. So the prices really went nuts.