Hmmmm. I remember (it's been yearrrrrrrs) that with the Rebels, I fared best if I gobbled up rim systems as fast as I could with my amazing diplomants, while keeping the Empire running around in circles with Han+Chewie and my other awesome saboteurs running interference within the core. If done right, eventually I was zooming into the core with insane fleets of something like 5 Bulwark Battlecruisers, with support. Though my first strike fleets would tend to consist of just 10-12 Nebulon-B, as they had an excellent combination of firepower and maneuverability, with 2 fighter squadrons apiece, and IIRC could carry some ground forces as well.
As the Empire, it seemed a fairly simple feat to get a couple battlegroups of Star Destroyers up, and bombard the living hell out of any dissenting core systems, hammering them under the iron fist of the Empire with ruthless efficiency. The key here was to get a very strong economy going, because it takes a lot of manpower to bring the rim systems under your thumb, with so much distance between the clusters.
I don't know, I thought that there was a great combination of diplomacy (fighting for influence on each world), subterfuge (few games have had such engaging covert ops components), and gorgeous (for 1998!) space battles. I definitely rank it as one of my favorites of all time, and probably the best game to ever be associated with Lucas Arts (though Ballblazer was SWEET back in the day
oh yeah, and Maniac Mansion and Zak McKracken!).