The Pirates are uber powerful now but predictable. I do not even try to fight them off anymore. I just build up sacrifical planets.
They always attack your closest planets. I do not invest in those planets anymore. No starbase, no research centers. I colonize them, build them to reduce the negative tax rate and then max the planet slots. I build LOTS of trade centers and hanger bays. I figure I might as well make as much money as possible before it is destroyed again. The hanger bays will handle the lighter stuff that comes to threaten them.
Once they destroy the colony, I wait till they leave, drop in that cheap colonizer that I have hanging one planet away and then restart the whole procces.
The pirates are now so powerful that unless you stash a large percentage of your forces nearby you are gonna loose. Period. It is not worth the loss in territory expansion opportunities to save something that is gonna be lost. It used to be that a decent starbase, a well placed defensive ring of turrents, and lots of SC support would chew up just about any pirate attack. No more. You max that starbases and all you are gonna do is waste resources. These pirates will chew it up so fast that you might as well have given you resources to the enemy for all the good it will do you.
Once I get into later game, I build a novalith or two and pound the pirate base back into the stone age. Then you do not have to worry about the pirate raids from that base anymore. If you try to take that base all you are gonna do is lose ships. Just detroy the base itself and the pirate ships that are there are goning to remained bottled up and no threat to you.
Tactics change with the patches. The pirates are too valuable to play without them. They are a realitively cheap WRECKING ball that you can use to knock the snot out of your enemies.