I may be blind...
But I can't see any crime rate value in my city view, where is this found and what scale does it use? (percentage??)

Mouse hover over the city. It is the next to last line in the info box.

Percent scale, but not sure what that is a percent of...

What exactly is the point of the crime rate? as far as i know there is no way at all to control the crime rate of a city.

Certain buildings increase/descrease it, like courthouses, dungeons, gambling houses...

But besides rather infrequent events (even with living world selected), crime doesn't seem to have much effect.

The traitorous literature event confuses me, personally.

But besides rather infrequent events (even with living world selected), crime doesn't seem to have much effect.
Expect more, especially more interaction with the Ratcatchers' Guild.