Just as a side note:
I've never found the "Star Destroyer" tactic too sucessful except on small-scale operations. Thos suckers are quite expensive and take a while to build.
By the time you build any significant amount of them, you're enemy has caught up or surpassed you in the ship-count category.
And once you've done 1 or 2, the enemy starts mining stars. Yes, I know, you send mine sweepers with 'em. But before you do, you may have lost a few to mines beforehand and wasted all that production you could have spent on warships.
Star destryers IMO only work like terrrorist activity; once or twice, they work. After that, their effectiveness diminishes significantly. Unless of course, you're fighting the AI.
IMO you're better off raiding systems and causing them to riot instead of blowing them up. Spend the production you'd use on a Star Destroyer to build a few small, fast raiding fleets. If you haven't tried that tactic, as said before, riots can bring huge empires to thier knees.