The Panopticon/Is The Feast of Steven valid?

Hello there. I don't think this has been discussed before so I wanted to ask the question of whether episode 7 of the Daleks' Master Plan (The Feast of Steven) is valid. I bring this up as the episode has little to do with the overall plot of the story. Even more a reason for invalidity though, I think, is that the Doctor breaks the Fourth wall at the end of the episode saying 'Incidentally, a happy Christmas to all of you at home.'

I was wondering if this hasn't being discussed due to a policy which says that part of a story can't be invalid whilst the other part is and maybe if this should be changed if there is. Any thoughts?