How useful are these numbers?
For a few cars I tested, I felt the Comparis valuation was a useful hint about an upper bound on price for either private sale or dealer.
The Comparis site gives car valuations.
It really depends on the car - for some their valuations are waaay lower than you'd expect to be able to buy for. My Landrover Defender, for example, comes in at around 15k, which is actually around what I paid for it two years ago, but it was marked down due to significantly less than perfect bodywork, e.g. not a single door panel is flat (they're aluminium, so it's relatively normal, and this had been used as a forestry vehicle) and there was signifiant rust in places like the steel joiners between upper and lower rear body panels. Finding one in top condition is going to set you back at least 25k.
It's a similar story for my R36 Passat, although not on quite the same scale, and of course I'm comparing its valuation with autoscout where many ads are from dealers, with a guarantee and new MFK, but the cheapest one I could find is about 50% higher than the Comparis valuation.
So it's probably not a bad estimate of the lower book value, but depending on the rarity, the real-world price you might need to pay in CH for a specific model might be much higher.