speaking of agent valour, I'm pretty sure this has already been asked a million times but what effect does valour on bishops/emissaries/princesses have, apart from making them more likely to resist assassination attempts?

also I'm quire interested in the "no-border-forts-but-spies" method...so spies alone catch & kill enemy spies/assassins? or does one need assassins for this?
in addition, do spies contribute to province happiness?