As the two above me said, wait for a Steam Sale and try out Galactic Civilizations 2. Make sure you play Twilight of the Arnor, as it is by-and-large the best version.
But to answer a few of your questions;
I've tried only one other space 4x Game and that is Endless space. I felt that the game felt rigid, traveling using space lanes in endless space felt really awkward in the sense there was no way to intercept ships without staying in orbit around a planet. Pirates felt horribly awkward often fielding more potent fleets than players in some circumstances.
Galactic Civilizations does not use "Space lanes" that ships travel across; all movement is unbounded, and most of the important fighting takes place in open space around "High-priority" areas with dense concentrations of resources, not in the orbit of planets.
Pirates are in Galactic Civilizations, but they are almost always vastly inferior to player forces and are relatively rare. The only exception t this is the "Pirate portal" mega-event, which spawns large numbers of pirates that scales with the map size.
The card based combat was absolutely horrid. There was a lot about the game that was unpleasant for me. Although i did get around 60 hours out of it before i decided that the game wasn't for me.
Combat in Galactic Civilizations (2) is purely pre-determined by the computer, but combat in Galactic Civilizations 3 may add some more tactical elements.
If someone could explain what makes the two series different that would be very helpful. I have quite a few friends that played GCII and told me to get it. Any help would be appreciated.
If Galactic Civilizations 2 is similar to any game(s), it is the Civilization series mixed with a small dose of Master of Orion. The main difference between Galactic Civilizations and those games in the economic system; you need to pay for production, it doesn't happen by itself and isn't self-supporting. This makes the game much harder to play effectively, and the AI will almost always outperform you in some manner because of the need to pay for everything.
If you would like a more in-depth explanation, then ask a more... pointed question; one does not simply sum up Galactic Civilizations :3