Oh I am interested in performing in some capacity just not as a concert pianist playing a long programme of pieces by other composers.I have immense respect for concert pianists but I think many pianists on this forum are pursuing a path that may never materialize in the way they may envision - I'd encourage people to explore improvisation and composition and realize that in many ways (especially for late starters and people with less prospect of performing traditionally) it could be more rewarding.I totally agree with you when it comes to the Chopin studies and Cziffra himself is actually a big influence of mine - if you look at his improvisations and transcriptions - they're full of borrowed ideas and extrapolations of pre-existing ideas. I don't think he and Liszt literally learned the entire repertoire! I think that they sight read many works and while they would commit some full pieces to memory....they would also perhaps also be thrilled by sections of works and then borrow and incorporate the ideas - be they melodic, harmonic, rhythmic, or in the form of figuration(like the Chopin studies).I have a feeling many pianists actually mess around with little bits and pieces like this, we all do, but I think instead of thinking it as a waste of time to only learn bits and chunks - we should look at it as a great time-economic way to broaden our musical and pianistic horizons.
In that my late piano teacher taught me to learn technique from practicing certain section of well-known pieces, I