Only the Advent has an offensive element, to there culture, which is by use of there super weapon. Culture is more of a defensive support, unlike the offensive pirates. The defensive part, comes form the fact that 9 out of 10 times, the culture of the planet, that you are fighting over, is the one of the person that owns it. This means that 9 out of 10 times, the bounes is for the defending fleet. A 15% increase to damage or a 4% increase in shield mitigation does seem as much in a ship on ship battle, but will seem much more important, in a fleet on fleet batttle. 15% times 8 = 120%. which means, that if you are have 8 ships and you have the culture bonues on your side, that your fleet, is dealing as much damage, as if you had 9 ships.
To me, it does seem a little weak. I would like it, if it was more like 30% damage increase and 8% increase in shield mitigation, but that is just me.
I'm also with Sakhari with the pirates. They is to stop, give your capital ships, easy exp targets, and are a money sink. The one thing that I have noted, is that while there Siege Frigates, are easy to stop, by a few turrents, there HC and other supports, keep on attacking any trading and refinery ships, which do more damage over time, to your econ. , as it take longer for you to destory them, with only turrents. A few attaks against a trade port or a few ships, does not seem like much untill you look at the fact, that while your main fleet was off in battle, the pirates, where attacking shiping, for 30 min. Which can lead, to a major lose in income.
But in the end, for the money you put in, the pirates, did not do as much damage, as you would of liked, to your enemys, econ. If they had a better AI or some more firepower, like a capital ship, could fix this, but I real don't have an answer.
The main problem is, that CULTURE, RESEARCH, and ECONOMIC only support you on the macro level, and can not get you the same results, on the micro. If you get all research for damage, it almost adds up to 90% increase(30% times three weapons system), but I only capital ships use more then one weapon type.
I do like how the military culture, economic and reserach VICTORY are all tied together, but don't like how three out of the four, only seem to only support one. It should be more equal in my mind.