Interesting note about Growing Up being written to make Frank seem less despicable. I always thought it was because they realized how CRAZY it was that the leading man of the show didn't have a solo (assuming we acknowledge that Not a Day Goes By is meant for Beth and was only sung by Frank originally because the original Beth couldn't sing it).
I mean think about it. Charlie and Mary are both explored early on with excellent solos (Like it Was, Franklin Shepherd Inc) that expand their characters, and also stack the deck against Frank by showing that he is a major cause of their unhappiness. Did they never think it was odd that the audience doesn't get an I Want song, or some solo from Frank to help the audience into his head and expand and explore his character? I can only assume that was on purpose. But might contribute to people finding Frank so unlikable. Then later in the show Mary and Charlie are again given major (mostly) solo moments that even further develop them (Now You Know, Good Thing Going). I think Growing Up comes a little late to really sway the audience about Frank, but thank god the leading man got a solo! :-)