You learn a piece because you are compelled to learn it. Most people want to learn a piece because they hear other people play it and thus want to be able to prove to themselves that they can also play at that standard. That is superficial in my mind. You learn a piece because you want to and you need to learn it full stop. If that is part of the OC or the whole thing (But I doubt that many people would actually like the OC in its entirity, parts of it is sheer brilliance, parts are just over the top ideas.)
Then again, I doubt many people have actually heard the entire OC or played through the score, so be careful listening to peoples opinions on it because it is just what they think, they don't actually know it for sure. Hamelin (if he did actually say it I don't know for sure I am only saying what others have posted) saying its not worth this time probably shows that he is not really interested in the music itself, not the fact that it is hard and time consuming (nothing would be too hard for him he has every tool in the book and outside of it!).