Is this one of our important tools that I havent been using?
It's an important tool everyone is not using. I think it's because most people just don't get in the position of fighting someone far ahead of them in the first place. It's probably a combination of difficulty level, and probably a lot of diplomatic shake-and-bake.
The trick with constructors is, they ARE ships. Think of those military assist modules as weapons. You normally spend 25bc for 1 point of attack--only to get it blown up if the ship dies. With a military SB, you're spending 95bc per constructor, times X constructors, it gets multiplied by every ship using it, and it does NOT die--the ships do. If you get only +1 attack on a fleet of just 4 ships, you already come out ahead. And if you're fighting a defensive battle, lots of ships getting thrown at you, you're going to get a lot more than that. While he's losing his big 435bc Battle Cruisers, you're losing 85bc Tiny hulls. The reason I say "constructors" and not "starbases" is, you can wait till the last minute to build the SB, so as to guarantee it will be used at least once. Constructors move; SB's don't. You can even move it into the stronger guy's territory, and use it to take out his orbiters.
Oh! That reminds me of another dumb AI exploit you can use: take out his orbiters, over and over again. If the Dread Lords were hovering their ships over your planets, what would you do? Not build defenders, right? Why complete it only to get it blown away the next turn? Not so with the AI--he'll just crank away defender after defender. While he's spinning his wheels building targets for you to shoot, you can pull even in research. If he's so far ahead in research that even his defenders are too strong, put down a military SB there. What's he going to do--send in fleets and counterattack? That's precisely what you want. I think the AI is rush-buying his defenders--it seems like every other turn he rebuilds one. So if you can interdict just a few of his planets, you can put a drag on the dumb giant's entire economy.