Yeah, they're indeed a very nice addition. Although I sometimes have difficulty with finding the logic behind them (or intelligence of the one who wrote it ...). Last time, I cleared a bandit camp with a secret cave, and in that cave was a diary which told about mutiny (2 actually) within the group. One of the mutiny leaders had apparently found the bandit leader's secret cave, so she nicely and clearly wrote in this diary how she moved her money and loot stash to an island not far away.
So let me get this straight. One of the mutineers discovers your cave, you replace your treasures as a result, and then you leave a diary
in that very cave which tells anyone who reads it where to find those treasures?!

No wonder there were two mutinies going on at the same time ... I wouldn't want to follow such an empty brain as a leader either.