I've read in Revolution in the head that Lennon saw the poster while filming promo video for SFF. I got Kevin's point, though. Still, I think that sometimes when you're out of it all, you can come up with very precise writing, which I believe Mr.Kite is, especially in the context of Sgt. Pepper. And the music helps greatly...
I find Good Morning, Good Morning in the same vein and also like it very much, because of the feeling of alienation that Lennon captures with his lyrics. And the ugly horns...
It's true, Lennon's writing and melodies on other albums may be sharper, but I think that on Sgt. Pepper he created something for album's sake, while being great on its own.