No I haven't... But I have played the demo on a friend's computer against the AI...
Sorry, but that really disqualifies you from making any argument at all.
As long as you haven't played against a human player, how can you be able to qualify what kind of tactics exists?
The current AI is brain dead. There exists no tactics against the AI because the AI is so stupid so there is never a need of tactics.
Increase the speed difference between many of your ships. Some ships should be extremely slow, and some should be very fast. As you don't want to slow down the gameplay any more, I'd suggest just making some of the ships a lot faster.
Try fleeing with a capital ship once in a while. You'll never get away. Because they are so slow compared to other ships.
Create harder counters for various ships. That is some ships should be completely DOMINATED by a bomber attack, some should COMPLETELY dominate against fighters/bombers, some ships should be destroyed very easily by missiles, some should be almost invulnerable to missiles, etc. That will force players to pay attention to which ships are attacking which ships. As it stands it doesn't really matter. Hard counters force players to start thinking tactically.
No!
Bombers are powerful enough as they are. (Try fighting some light carriers and a Sova if you have no flak frigates.)
It already matters with what you attack.
You would be surprised how powerful an early Carrier attack is. Or how hard large group of LRMs hit against not only defenses but also against light frigates and low lvl capitals.
Add some special "modes" that ships can be in... For example, pumping more power to weapons and less to engines or shields, or more to shields and less to everything else, or more to engines. Those are just some mode ideas off the top of my head. You should try to think of something more original if possible... I'm sure others here will help if asked.
Did somebody say micromanaging?
I already have enough to micro with the capital ships abilities.
Each race needs a siege weapon. As it stands each "gravity well" is it's own little map that can very easily be turned into a little castle. What is needed is a weapon that can be fired from one phase jump away that can damage defensive structures and perhaps ships without risking itself. It could be some big late game unit that camps next to the phase lane to the next system and then fires something into phase space... To counter this you could force the gun to only work against defensive structures or structures that have been previously scouted.
LRMs are your friend. Also if possible, space superiority with fighters and bombers.
Only thing that needs change here, is that the build radius has to be made smaller compared to overall grav well radius, since currently if you build near the enough to the edge, large fleets jump right into the gauss cannons range.
I proposed the Conquest Supply system a while back; not many thought they would be interested, though it was brought to my attention that this should be relatively easy to mod into the game.
Uh, no, it's not possible to mod it in.
Something the game REALLY needs that it doesn't yet have is big splash damage weapons. Some kind of weapon that doesn't really target a ship per se so much as an area. Such weapons would probably need a high AM/supply cost or high cool down to prevent spamming. I personally favor high AM/supply cost... they would be very effective against small lightly armored units but do almost nothing to larger units. unless you got a direct hit... then they'd do good shield damage but shouldn't ever really harm armor that much. These weapons would be most useful in dealing with clouds of bombers, fighters, perhaps these sensors/jammers, and should do respectable damage to frigats.
Somebody asked for LRMs?
Something I've noticed is that almost anything that damages shields does even more damage to armor. The difference in damage to shields and armor should be increased. You might consider making this a weapons fire mode... that is different types of ammo or whatever. Or you could have ships specialized in shield destruction while others are specialized in armor destruction.
That's because shield mitigation works on a percent base, while armor works on a flat bonus base, making shields much better against high damage attacks.
You take that out and unit choice becomes almost irrelevant. That not only hurts tactics but strategy as well. Because the types of units used matter less... if they matter at all. It's sloppy.
Ok, you play against me. You only build Cobalts, while I build a mixed fleet. Let's see who'll win.
Hat tip, it will not be you. 
Why do fighters hurt frigate armor when they're designed to damage other fighter craft?
Did you check how much damage fighters make to frigates? Almost none, that is how much.
No, because the enemy can turtle in some choke point system and with a bunch of bombers sitting on top of the phase lane all the gauss cannons placed on that one part... to say nothing of having a few capital ships.
Ok, I had a game where only one enemy (human) was left. He built a dead asteroid up to a fortress. Gauss cannons, repair stations, hangar defenses, flak frigates, 4 capital ships. About as good as one can defend something currently.
What I did was the following, first my ally jumped in with his carrier, destroying his fighters (although loosing its own fighters to the enemies flaks), then I've jumped in my LRMs and flaks. Now the enemy had to move out to engage my LRMs with his capitals, as soon as he did that I've jumped in my own capitals with support ships. My LRMs killed his gauss cannons, the flaks killed his bombers/fighters and my capitals and light frigates killed his capitals.
Battle won. Now tell me, I didn't use tactics.
No, it was a space game where you had perhaps 4 to 8 ships. It tried to do space tactics but ultimately failed because most of the choices you could make with ship modes etc didn't matter much. There was a big carrier the humans had that could generate a "fortress" shield. The shield was pretty powerful but it was mostly just huge. You could keep most of your fleet in it without a problem.
But Sins is not that type of game. Sins is not designed for "small squad" tactics games. Sins is designed for large battles and is much more about the economy of war (resources and stuff) than about microing all your battles. (Although micro is still very necessary with the current unit AI.
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