A difficult question.
Would I want to? No, of course not. I would rather earn flying however Blizzards says I have to earn it in the game.
But, let us just say for a moment, that I saw in the store that for 15-25 bucks I could get flying and it was the absolute only way I was ever going to get it in the game. If this happened to be the case.. yes.. I likely would purchase flying just so I could have the convience.