Options should be meaningful though. And as it stands, if you want to defend a starbase you are better off building N warships and stationing them at the base than N constructors to improve the base firepower/defense. And it's not like it's a close call or anything, it's that one option is so stunningly better than the other, that the second option is nothing more than a trap for the unwary.

Do starbases still have modules that provide bonuses for attack and defense?

Given that defenses are going to deplete as they get attacked, maybe a solution would be to quadruple both the base starbase defenses, and the value of their defensive modules.  That would definitely make them more of a hazard, both on their own, and with a defending fleet to support them.

I'd have to argue that the strongest fully upgraded starbases should be expensive, but offer some degree of defense as to justify their cost. They'd have to be as powerful as say, an upgraded weapons starbase in Sins. Able to stand up to a moderate fleet.

That and offer something that you cannot ignore as an attacker. Ex: Maybe lots of damage to ships within their radius?

To be honest the modules or whatever should depend on what technological era your in the best modules should be for the last technological era. Just like it takes a long time to research huge hulls, weapons, or defenses it would take a long time to research your best defence and offence

In GalCiv 2 Dread Lords, I complained about the lack of defensive ability for starbases. After upgrading a starbase to max (including researching all techs to do that), they were not well suited to their own defense. Fleets could be made that could kill a fully upgraded starbase. It was better to keep a fleet on the same tile to defend them... if you even bothered.

It became worse in Dark Avatar when the combat system got changed and starbases did not get improved to take advantage of it. The changes was from all ships being restricted to 1 attack per round to as many attacks as the ship had weapons (so a ship could kill multiple ships per turn). Starbases never got more attacks. Likewise, the changes to defenses was from defenses working at full power for every attack (so if a ship had a weak attack, it would practically be useless against a well defended ship) to each attack would weaken the defenses of a ship to 0. Starbases didn't get stronger defenses. They became vulnerable to fleets of many ships as they couldn't kill them quickly and their own defenses could be weakened to 0. Further more, ships got even larger, so you could eventually build huge ships that could out class any starbase combat wise, let alone what could be done with fleets.

It became even worse in Twilight of the Arnor. You could now add HP boosting modules to ships. You could add fleet modules to ships (for both attack and defense). Some of the tech trees got remodeled in such a way that some starbase modules got denied to some civilizations. Hell, in some cases it looked like it was remodeled deliberately to have some modules harder to get access to (and became nearly useless by the time you got them).

Overall, I found that starbase defenses were not worth while beyond the basics. If you went for the early bird advantage, it might be useful for a while (if you got it just right, enemy ships would attack on mass and be destroyed in a futile attack against a tough nut). Ultimately, I found that it was best to use ships to defend starbases, namely mining starbases for galactic resources and economic starbases for planets. I found influence starbases to be useful for a time, but it was something to be disposed of once I finished culture flipping a planet or securing the influence in a region through other means. Military, well, I never mastered their use, and many of their modules were the ones that were made harder to get in Twilight. Terror Stars, its best to forget about them.

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In GalCiv 3, the ability to have fleets team up with starbases is a nice boost. It is also a nice boost that fleets with starbases (or planets or shipyards) can exceed normal logistics early in the game (it is 40). Further more, since sensor ranges don't have a limit in this game, it is possible to see attacks coming (and do something about it). It seems that stardock has continued to leave them the support role. They can be defended, but they can't be expected to defend themselves. What advantages they offer is the real reason why you build them.

Right now a military starbase can add a pretty hefty movement penalty to all enemies in a 9 tile radius, while halving the movement cost of your forces and giving +4 to all weapons and defenses (those values can be further boosted by modules that specifically boost certain weapons or defenses).  It gets particularly potent when you have multiple military starbases with overlapping areas.

Still, to defend those starbases, it makes much more sense to have a fleet of tiny fighters using the movement boosts to quickly intercept attackers and win with the weapon & defensive buffs, rather than giving the starbases defensive boosts.

yea, they aren't really for fighting or defending in combat directly. I think balancing is difficult to, as it took some months of testing to get it right in the galciv2 community patch. So far I like most of the bonuses that starbases give, they seem balanced and I like that we need ships to defend them properly.