One thing that I think could add further to the strategy of Galciv II is the ability to add escorts as part of the fleet system. The basic idea is that a few ships that are faster than the "core" fleet could engage attacking enemies without putting the main ships in the middle of the fight, thus allowing you to get your shiny new battleship to the enemy homeworld without so much as a scratch. This escort would still take up logistics, and would join the core fleet in any attacks. This could allow you to build fighters that protect your freighters, colony ships, and large transports without having the ship being escorted die first. The escort ships will have to be faster than what they are escorting (so they can intercept the enemy fleet), and this will help balance it out by giving them slightly less room for weapons.

Now, onto carriers. One thing that could also add some more strategy would be a carrier module. This large, extremely expensive module would make a ship act as a "home away from home" for your fleets, by extending range and conducting fast repairs. The range should not be like a starbase, but more like a one tile radius that is increased by one tile per level of life support on a given ship. The carrier module itself should contain a large life support value (it causes the ship it is on to provide it to other ships, after all). This module should be very large and even more expensive, so a carrier will be a large, valuable, vulnerable asset to the fleet, since a carrier equipped ship should not be able to hold enough weapons to fight off a real attack.