Images are allowed, but in moderation. The point of this wiki is to provide information. I don't think there is really anything that can be added to pages like this. I think magazines can be a great resource for articles, but they're are not substantial enough for their own pages (a general publication yes: Shojo Beat). I don't see the relevance of listing them on the artist page, there are 52 magazine covers on Mano Erina's page... There is too many images on pages like this; see how information ends, but the page is still stretched because there are too many images.
I have brought this up on the forum and the in the Photobook category, please feel free to weigh in. Still waiting for another moderator to join. For now I would say photo books are allowed; although I personally only feel like ones of some kind of cultural relevance such as Amuro Namie's 19770920 or Kuriyama Chiaki's controversial Shinwa Shoujo should be created, as there is nothing to really be said about a regular idol photo book. As for the calendars, they don't need their own pages, but I think it's fine to leave their covers on the artist page.