Unless the end goal is really just to keep the turrets ALIVE rather than just ensure they are as effective as possible, I still feel that my suggestion of giving them an AOE explosion on-death is more true to their form and function (after all, there are a bunch of flak canisters inside the turret, arent there?).
Lets say the on-death explosion does as much damage as, oh, say 4 salvos from the turret, then even if they die right away, that would give them the ability to put on 5 salvos worth of hurt on a group of 2000+ laser gatlings coming in as a wave without needing to partner them with masses of grav turrets, tractors, or force fields. It also provides the added benefit of not requiring any extra opportunity cost (knowledge, cap usage of other defenses) to achieve that extra effectiveness people want from them. I personally think it would also give them a "cool" factor. =)
Needing to partner them with forcefields to keep them alive means I would have to, well, put a forcefield over or near an incoming wormhole, which is something I dont do, and still wouldnt do if that change were to be made. Especially in light of the new exo-waves, my defensive style is rather to use FFs over outgoing wormholes, and changing up the flaks to be able to fire 100% from under them isnt nearly enough to make me want to alter my FF cap usage.
Edit: You could even lower the attack priority of the AI ships against flak turrets, if they have other options, since they know they would blow up and hurt them. And wouldnt you know it, that would help keep them alive. =)