If you think you need a cadenza to make a composer...
Schumann is one of the greatest of composers (well, fine, so there's many of them, i stand by my point). I don't think a composer should try to experiment with more styles then what they want to play with. And really, Liszt was one of the very few composers who experimented so much, and in many ways it wasn't so very successful. Schumann also experimented, just not in the same way that Liszt did. Also, don't equate cadenzas with experimentation - in fact, when Schumann didn't write cadenzas, that is MORE experimental than writing them. After all, Bach had already written out cadenzas as well as improvised them, and so had Beethoven, Mozart, Chopin, Liszt, Handel, Haydn, and all the composers before. And in Schumann's structure of music, he's in fact much more experimental than most of the composers before him - who else wrote small collections of pieces like Papillons or Kreisleriana etc.? His ideas with some of those pieces actually led to the development of the tone poem. His music is like variations without a theme.