I really liked your reply Bernhard. I am also interested in playing 'popular' music and two books that I find helpful are both called How to Play From a Fake Book. One is by Michael Esterowitz and the other by Blake Neely. I am thorougly enjoying this approach to music as opposed to only classical.
Playing popular tunes is not a "second best" musical activity. I think that to do it really well demands a much higher order of musicianship than it takes to play a Chopin study; no doubt many would disagree.
Bernhard, are there any recordings of kissin or hamelin improvising, and if so, is it really good?