Yesterday, I read a blog post from someone (I can't remember who but that's not really pertinent) where they hadn't written their morning pages because things were not that different with each new day.
In my mind that's the perfect time to be writing them, to deal with the frustrations of similitude and see what thoughts lie hiding In the undercurrents of the mind. These thoughts, by their own volition, may change things.
Morning pages aren't a diary, a record of what has happened; they are what might be, the extreme possibility of the subconscious. That's why the words must flow of their own accord or one becomes stuck trying to think of something to write rather than just writing.
Conscious decision making should not factor into it.
What's on the inside, the raw ideas and emotions, that which is waiting to come out, will always be different no matter how similar the day.