I could justify music for Shostakovich 2. Contemporary music is difficult enough to memorize as it is, and when you consider that you have to know the orchestra part too, it's only rational to use the music if you're uncertain. Clara Schumann, notorious for being the first to play music from memory, always played concerti with the score as a courtesy to the orchestra. If the soloist messes up, it's easier to fix if the soloist has his score to search. Otherwise s/he could end up at the conductor's stand, looking through the full score to try to find a spot they could agree to restart at. (That actually happened to one of the great pianists, but I can't remember who it is now.)
As for your playing, I agree with memorize Liszt, use music for Messaien.