I appreciate your concern, but I gave up on La Valse due to its difficulty. I find it rather awkward for the hand.
I've played 'Valses nobles et sentimentales' before and thought of moving forward, so I gave up on the idea of playing other Ravel than 'La Valse'. I sight read through Brahms Sonata No.1 and Chopin's Second Sonata and I simply can't decide. Both seem a challenge and I'm not aware which is technically/musically/learning-wise easier to grasp.