If you want to increase the ammount of pirates you get you can change the fleet supply requirement for pirate ships. From what I have seen so far with messing around with my pirate info is you can only have 5 types of ships max per raid composition. They also need to be frigates (Haven't been able to get cap ships to spawn under the cap ship stat). The weight determines the chance of that ship showing up (Not 100% sure on this it might just be like a dice roll and moves down the list till it gets a success then repeats till the fleet caps used). I have also made my raids harder by making frigate cap ships, so I end up getting a mix of about 10 sova's/kol's showing up at my doorstep with a fleet (I used a few of the dead ships from sins, also you can add ships with command points to allow pirates with fighters).
I made a quick change to my raid composition and changed the min raid strength to 300 and changed the pirateheavy to require 100 supply to test this and only 3 pirate ships show up.
An example of my final pirate raid composition (Mod used Solar Sins 2.0 for v1.1 modded)
Hope some of this info helps in making the pirates more fun.