Sakuro:
The journal aspect isn't something I'm all too keen on. Never liked journals. They let people get a glimpse of what is going on in your head; which is probably what you're after. Every time I read a book or seen a movie with someone in it that kept a journal, that journal was used against them or the knowledge is abused. My personal experiances with journals aren't much better. Its something I'm willing to try, just so long as it isn't required.
To me, part of the point of a horror game
is to have your personal foibles used against you (in an IC way, of course). A good GM uses the info in a way that enhances the psychological impact and emotional turmoil, in a way that's "fun" for everyone involved. If that isn't the kind of fun you're looking for in a horror game, what kind of emotional turmoil did you mean?
I like seeing glimpses into characters' heads in general. It makes the game richer, both to play in and to read. It makes the characters more realistic and sympathetic. It also provides feedback to the GM so they have some clue how well they are conveying what they're trying to convey, and helps them decide what to do next that would be the most interesting to the player. It helps keep everyone on the same page.
On a different note, I've been playing for Dante in particular for a while now, and he's always been good about not abusing glimpses into characters' heads (except in the good way described above). I've often included PLs that describe exactly what my character is thinking, and why he's thinking it, and what he wants to do about it, as notes to myself so I can keep track of things for later. The most he's ever done with them to me directly is speed up or slow down the scene, for example if he knows I'm about to barrage an NPC with a ton of questions one at a time.
So getting back to Hunter games in general. I'm all for emphasizing the personal horror, and the journal idea sounds like a good one to me to help set the tone and keep things on track.