seems everyone wants pirates to be able to pull some godly desperate last trick out of their sleeves.
they are scum of the galaxy. they use salvaged ships. they do not have any kind of non-monetary backing from any nation.
I'd agree with the 'scum of the galaxy' notion... but it can be useful to use such 'scum' to do a nation's dirty work with a lower chance of showing its hand. Providing actual ships or access to bases would be rather blatant, but the odd bit of funding, technical data, intelligence et al might be useful.
If I were planning a rework, I'd want them to be more pirate-y and less periodic-suiciders -- in the current build, they'll blithely attack even an Advent desert planet with max'd tactical slots, a Transcendia, and a capital ship parked just to earn XP. In other words, sneaky, theft-oriented hit-and-runners instead of attempting brazen assaults on warships and heavily defended systems.
- Nix the periodic timer motif. Activity would be ongoing, although not necessarily of uniform intensity.
- Payment mostly pay-to-avoid-being-hit; pay-to-hit-someone-else could be offered. In the latter case in particular they wouldn't necessarily follow through. They're scum, after all... and they wouldn't warn the galaxy who to expect them. Being self-centered scum, a wealthy, well-defended nation that is paying them off should be attacked much less often than the intended victim if the intended victim is substantially more economically interesting and less fearsome.
- Smaller craft strongly resembling civilian vessels (trade ships et al). In fact, give them a high probability of masquerading as civillian ships until they attack, and resuming some time after breaking contact. Ship design -- emphasis on speed; possibly later on PJI immunity. Ability to raid extractors, turning them neutral and seizing resources; ability to pillage resource asteroids and demolish those extractors.
- Ability to operate from 'neutral' worlds. Hey, they've got money and they're not trying to overthrow the local government, unlike those fascist traders, religious maniacs, or alien slavers. 
- Primary targets -- civilian ships (getting value based on type/cargo), undefended or weakly worlds particularly asteroids (robbery/tribute, loyalty hit). They should be avoiding anything resembling even-odds combat, since they want to die rich, not nobly and dramatically.
- Raiding labs to steal research points.
- Technological development for them would be somewhat limited, but some obvious paths would be --
- better masquerades (possibly eventually to fooling mines?)
- more speed
- PJI immunity
- more effective raiding parties (faster hits on facilities)
- better intelligence gathering (as in visbility into other empires)
- possibly, ability to temporarily disable tactical facilities (via raiding parties)