@Tamar The Ankh-Morpork Archives are a reprint of the content of the diaries - I've just finished reading Vol 1 which contains text from the UU, Assassins, Thieves and Post Office diaries. It's pretty good to have this content reprinted, and the art pieces are larger than they were in the diaries.
These new journals from the Discworld Emporium are something different. I got the Death journal from last year. It's not a diary - it's mostly just some brand new art (by David Wyatt, IIRC), and some quotes from the books, with a lot of blank pages to be filled in as a journal (rather than as a diary). And although the art is lovely, a lot of it is repeated throughout the journal (I'd guess maybe 20 different pieces of art?) and to be honest, I'm not sure it's worth the price tag they've attached to it. I'm presuming the City Watch Journal is along the same lines - some new art, some quotes, and a lot of empty pages...