I agree with your idea: a rating system might be simple to do, but could be a huge work if your collection is quite large... imagine rating 5,000 songs!

An intuitive/predictive rating system is what Empeg deserve. Maybe playing state could be divided into two mode: normal and predictive, further divided into Auto and a sort of 'mood selection'.

Of course it would need some apprentice period, and I see some problems with other persons in car: what if your friend hate a song that you love and skip it?