The vices thing is not really substantiated so it may not be true. I'm aware of how spies currently work and I always place a spy in each of my provinces. They changed it so that I only need one spy per province.

I forgot which campaign it was, either the Danish or Hungarian campaign. During that campaign, however, my Middle Eastern Holdings had a drop in loyalty and went into the red and orange after they got cut off due to an enemy blockade. This was around at least 5-10 years after I captured them. The annoying enemy ship kept moving also so it took a few years to destroy it and they usually had a new ship soon after.

It's usually not a problem but you never know when a king with +30 happiness in all provinces suddenly croaks. Also, it takes more than 10 years for a province to assimilate which I find to be a problem even when I'm going slow.