in "The Wizard and I" Elphaba: "...and I swear someday there'll be a celebration throughout Oz that's all to do with me!" also has to do with the song "wonderful", taking place later Wizard: "Someday there'll be a celebration throughout Oz that's all to do with you!" Elphaba: "That does sound wonderful!" I think those lines are sad, because she was right; there was a celebration that was all to do with her, but it was to celebrate her supposed death, rather than her being great and important to the happiness of Oz. :(
And also I caught this: In "Sentimental Man" : Wizard: "Since once I have my own day in the sky..." Elphaba: (chanting from grimmerie) "Ah may tah tay may tu se say ta!" Wizard: "I know everyone deserves a chance to fly!" Later in the song, when Elphaba discovers his trap to use her: Wizard: "I know everyone deserves the chance to fly!" And, of course, in Defying Gravity, Elphaba sings: "So if you care to find me, look to the Western skies! As someone told me lately, everyone deserves a chance to fly!" And she quotes the Wizard, but then she sings this: "And if I'm flying solo, at least I'm flying free! To those who'd ground me, take a message back from me! Tell them how I'm defying gravity! I'm flying high, defying gravity! And soon I'll match them in renown. And nobody, in all of Oz, no Wizard that there is or was, is ever gonna bring me down!" So, the song is about her defiance over the wizard, it seems, yet she quotes the wizard, but i think it makes her realize a little, that she wouldnt get to fly without remembering the wizards words and being inspired a bit by them, but it also proves her point that the wizard caused her to defy gravity and get away.