I'd personally rather see Missile Turrets get higher knowledge costs than see the Spider Turrets get lower knowledge costs. Mostly because the range on the missile turret is so much greater than the range on any of the other turrets without costing it a significant amount of DPS when compared against the Basic, Laser, and MLRS turrets. Plus, the Spider Turret is in some ways more of a utility turret than anything else.
I disagree with this. Aside from the laser turret, which needs around 200k bonus dps, the missile turret does as much damage as the cheaper and much hardier basic turret, and is well behind other turrets in damage now.
I think that just buffing the K cost of it will accomplish the same as it was before: it will just be ignored by most. I'd rather actually addressing why it is used so much more often. They aren't really good compared to others right now. Missile turrets got hit with a whooping 36% basic dps drop.
The only reason missiles are good compared to snipers is because snipers hit with only 65% of missile damage.