Strangely, I've been finding Artyom's current thoughts written down in places he's never been to. Ignoring how ridiculous that is, does finding these notes serve any purpose other than enriching the story?
21 Answer
As Draedalus mentioned, there are alternate endings which you can achieve by doing "good".
However, collecting his notes isn't counting as doing good, so this has no influence on the kind of ending you will see.
Here is a guide that tells you what to do in order to get an alternate ending. Notes aren't mentioned there.
