Some testing numbers on missile damage and cost efficiency (as compared with large cannons). These tests were performed on ship internal components that allowed missiles to fully utilize splash and cannons to fully utilize penetration.
Results : - - - RC3 - - - RC2 - - - Stable
Cost/DPS - - - 5.12 - - - 6.56 - - - 3.22
Cost/DPS - - - 3.17 - - - 3.17 - - - 3.17
Surprisingly, missiles on stable have worse cost/dps than large cannons, though only slightly. On both RC3 and especially RC2 missiles have far worse cost/dps than large cannons, even before factoring in the huge cost-efficiency of point defense.
I think we need to stop viewing missiles as a ship-killer doomsday weapon. Their actual damage is fairly low when compared to the other AOE alternatives - large and small cannons - even on stable and absolutely on RC2&3. Their shield damage is even worse - 3 large cannons = 2 shields but 5 missile launchers = 2 shields. That makes missiles more than twice as expensive at taking down shields compared to any other weapon in the game.
Where missiles do shine is in their indirect fire, splash through shields, and long range. Frankly, I think that's a good place for them to be.
As for PD, even the heavily nerfed PD on RC2 manage to be nearly 5 times as cheap as the missiles they counter, on top of having a huge coverage area and the ability to focus fire. Even if PD was significantly worse vs wrap-around missiles, PD vs missiles would still be incredibly effective.
This is the interaction I'd like to see between PD and shields:
PD: Huge coverage area. Very surface-area-efficient vs missiles (but expensive if they're only used to defend a small area).
Shields: Small coverage area. Cost-efficient vs missiles for the area covered (but not cost-efficient to coat an entire ship with, and not surface-area-efficient since they'd need to be mounted forward to prevent splash).
PD would be good at defending the vulnerable sides or rear of a ship, and would be a great supplement to shields to help and counteract focus fire with their huge coverage areas. Shields would be solid against missiles if you already need them to cover areas against other weapons, but they would be way too expensive to cover your entire ship with.
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Tests were performed with a single launcher/single cannon firing at a giant square of power storage. Each test lasted approximately 30 seconds, with 3 test on Stable and RC3. RC2 numbers were calculated based off of RC3 numbers. The missile launcher was given 1 factory, 14 crew and put in it's own compartment for optimal fire rate. The cannon was given 2 factories 8 crew and put in it's own compartment for optimal fire rate. Reactor costs were not factored into costs for either missiles or cannons. Only 1 2/3 ammo factories were factored into costs for the large cannon. Tests were performed on the stable version and the RC3 version - the test version crashed every time I tried to start or load a game.
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Walt
I don't think that 18 pd vs 14 missile launchers is a very effective test. 18 PD only costs around $80k to operate, while 14 missile launchers costs ~$450k (on RC3) or ~$575k (on RC2/stable). Even a 33% shot-down rate is pretty high on 15% of the budget.
I would also like to point out that your test had PD distributed onto different sides of the ship, meaning the PD isn't all active at once. The missiles tended to all focus on 1 or 2 ship sides which significantly reduced PD effectiveness.