My friend and I played a massive 5 star map 2v6 hard AI's yesterday and I thought I'd share my thoughts. I played as Advent.
Mines:
Advent mines were really useful early game. All you need are two military labs to research mines, and drone cruisers and you can pretty effectively counter a frigate or capital ship rush. A couple of drone cruisers can lay mines on your frontier colonies and move quickly to defend with fighter squadrons - with a few seekers and illumniators, drones and mines make for a pretty decent defense - especially since mines cost only time and micro (two things you typically have a lot of early on).
Advent mine fields definitely have diminishing returns to scale. Even if you take the time to distribute hundreds of mines (very micro intensive) in a gravity well, the first fleet to come through will clear most of the mines either by detonation or getting the mines to case them across the gravity well. It may be that you only need to stop that first mid game attack fleet but a smart opponent will send a small fleet of frigates ahead of a main attacking force to move the mines out of the way.
Late game advent mines are pretty much useless. They don't do much damage against upgraded ships and they take too long to micro in large enough distributed fields to matter much. They can be used for near planet defenses to take out planetary bombardment frigates and do some damage to capital ships but that's a bit of a stall tactic. In all likely hood you will not be able to replace those mines before enemy reinforcements arrive.
One tactic I didn't try out was offensive mine laying with drone hosts. I'd be interested to see if using mine fighters to lay mines near capital ships and cruisers is an effective tactic. Mining the areas around enemy frigate facilities and capital ship facilities might be effective as well as mining the phase lanes deep inside enemy territory.
Long Range Cruisers:
No real point in rushing to crank these out early game, unless you a know you are playing someone who likes to turtle.
Mid game: I'd rather have the two extra guardians than one starfish in my mid game fleet. A few starfish are helpful in taking out early star bases but an extra capital ship is just as effective and comes with more versatile uses.
Late Game:
Starfish are really good at taking out clusters of labs, defense platforms, and resource structures but they have to be in force and microed well. Their range isn't much to write home about and the AI doesn't acquire new targets after the initial targets are destroyed. They are pretty weak and expensive so I prefer to use them to take out every thing but the star base, let 50 or do bombers soften up the local star base, move in the capital ships and cruisers to give the star base some thing to shoot at and then bring in the "starfish" to help bring them down faster. In general I don't think they are worth the money and micro effort. I'd rather use the Advent Heavy Cruisers and bombers to do the same job.
Star bases:
In general I am dissapointed with advent star bassesas they don't really integrate with the Advent Fleet or structures that well. The nice thing about advent is how well the fleet comes together as an effective fighting force through complimentary abilities - and the advent starbase doesn't really fold into that design paradigm.
Advent star bases can really only effectively engage about 1/3 - 1/4 of any planetary gravity well. You can position it near the planet but you will allow enemies to fly around the base or it can guard one maybe two phase lanes (depending on geometry) and leave the planet largely unguarded.
In small non-settlement gravity wells they are really effective as they can dish out punishment everywhere but they need to max out their armor, and weapons to be there for very long. Late game they wont stand a chance without a defensive fleet to help.
Early Game: Rushing a star base is expensive. It might be effective on small maps to bottle in your opponent after some sort of rush but in a large map scenario its not that effective.
Mid Game: A star base at a new settlement with the allegiance, culture, and or merchant upgrades can really help boost the Advent Economy. They can stave off a mid game attack with help from a defense fleet but you will have to choose between econ/culture upgrades or weapons/armor upgrades.
Late Game: The Advent star bases are really just damage sponges. once the enemy has a large fleet with 15-20 long range cruisers the star base really doesn't stand a chance for more than a few minutes. The hangar upgrades arnt really worth it unless the star base is in a non settlement gravity well. When an invading fleet has 40+ bombers the paltry 8 fighter squadrons just arnt going to cut it. Its better to spend the money on hangar defenses (which get shield and squadron upgrades).
