Ok, so some people enjoy that event, some don't. Personally I hate it. It always happens when everything is running fine, as if the programmers thought I'd be bored in that situation. Why not create a mod or something to deactivate that particular event?
Btw, it's not that I want nothing happening to me, I enjoy an occasional pirate-fleet destroying half of my stuff

But those little vengeance ships are just annoying, they never managed to hurt me at all, they just make every turn last an hour (not because my hardware can't manage them, but because every single one of those 5000 ships attack some random outpost of mine without the slightest chance)
And yes, I do use spies, happens anyway, preferably with my best allies, which just makes it more annoying, random and stupid.
That event is the ONLY one that gets me to ALT-F4 this great game.