Well, I never really build turrets, but I can see a situation where someone rings the planet with them at low orbit to protect against siege firgates, and the point of an upgrade which would then allow siege frigates to fire from outwith turret range. I have no clue if the upgrade is significant enough to allow for that, since I haven't built siege frigates in ages (though I have been trying them a bit with the latest patch). If I use anything it's hanger bays with fighters to protect from siege, and against that extra range does nothing except a slight dps gain (if you are comparing damage to time-in-system). So, yeah, still with you on the upgrade being pretty damn worthless.