Pirate Diplomacy has a bit of a problem, and in turn this makes for a problem with one of the Vaulters schticks. It doesn't last- the Pirates are doomed to fall, inevitably, and they're doomed to be bribed into complacent paralysis long before then. They don't do much in the current design, and it makes the major mechanic of the Vaulters DLC a bit flat as a result.

In addition, the ability to bribe them into compliance leaves the Vaulters, the faction theoretically best suited to diplomacy with these rapscallions, better off destroying the Pirate League ASAP than actually cooperating. Corsairs cannot attack enemies at peace with the Pirates, and peace with the Pirates is frequent, so it's a dead trait for a long time until the Vaulters kill off the Pirates.

After some chat on the Discord, I see a few simple solutions to this that require less work than a full overhaul:

1. No immunity for Max Relations, except for the highest Relation (Pirate Sovereign, essentially) and Corsairs (who are, of course, fellow Pirates)

2. Stage 2 Pirate League, a separate Pirate League which spawns on Special Nodes at a certain point in the game, or after Fluffpetal's capture

This way we can still get our unique Pirate Hero, and the Pirates are still only a minor threat in the early game; however, they will eventually become a greater threat, capable of spawning on Special Nodes at any time, which unlike systems will remain unsettled all game, and thus will never "run out." This way Pirate Diplomacy becomes more useful and has greater longevity, and Pirates as a threat become something more serious and recurring as wiping them out no longer guarantees that they won't return.

This would hopefully breathe new life into all of the mechanics of the Vaulters DLC, whose mechanics currently tend to get shut down too quickly to have any effect, often becoming less threatening than vanilla Pirates simply because vanilla Pirates cannot be bribed into compliance.

+1 on this. At least, all the Non-Agression Pact should be abolished after Fluffpetal's capture, allowing pirating other empires without restriction.

And I also agree that NAP should have limited effect or limited coverage. It should be either A) allow attacking an empire which already has a NAP with pirates when you pay pirates some cost or lose some standing with pirates or B) make harder to enact NAP in ways like limiting the total number or putting costly upkeep.

...I've had Pirates spawn again after catching Fluffpetal.

I'd also like the stage 2 pirate league to have a carrier level ship that makes their fleets far more of a menace in both space and when invading. ATM Pirates don't really do much even if they have multiple fleets orbiting and invading a planet (in part because their fleets manpower is so low) and it really makes them a minor nuisance that isn't worth dealing with. 

I've rarely, if ever, seen a meaningful Pirate comeback after Fluffpetal is captured. I question whether I have at all, but assume that it is possible, but doesn't really occur due to the galaxy crowding out any legit systems to spawn a pirate base from. The whole point of Fluffpetal is that the League has been wiped out.

Adding Pirate carriers would definitely be a nice, though not completely necessary, aspect of a Stage 2 Pirate League. The League would hopefully have much higher power gains, and much more efficient ship designs, so they're a greater threat over a shorter time frame.

And hopefully resource modules like Titanium guns, if they could still inhabit colonizable systems.