Yeah, the turrets can only be turned on or off, or have their targeting data cleared so they shoot any target that gets in range. And I second that statement about them being weak. They're really only good as a distraction, or against melee-only targets, when the targets can't reach the turret.
Now, if there was a high science skill option to alter the targeting data so they target only the group they once ignored, that'd be a bit better. Oh well, missed opportunities and all. :/