I've already explained my position on CIWS, but I'll say it again - CIWS are awesome. They provide redundancy and economy of self-oriented PD solution. You are right when you know that the ship in question will not be left alone. Or won't be doing Jump Point Assault. For those situations CIWS is crucial, IMO.
I'm almost done with my next generation designs and I think I'm gonna omit the usage of CIWS for now, but I still do see a great value in such system and will most likely return them to service if I may end up designing ships for Jump Point Assaults. Or get swayed by my own combat experience. We'll see.
I've never used CIWS for jump point assault PD...you may have a point there. But as general purpose PD, I'm not convinced by the redundancy argument UNLESS the ships are expected to operate solo.
My understanding of your position (correct me if I'm wrong) is that adding CIWS means that even if the ship loses its fire control or sensor, it still has some PD capacity. The thing is, if you have two ships in company with 2 gauss cannons, 1 sensor, and 1 fire control each, the scenarios are as follows:
No damage, all ships get x4 gauss protection
1 ship loses active, all ships get x4 gauss protection
both ships lose active, all ships get no protection
1 ship loses fire control, all ships get x2 gauss
both ships lose fire control, all ships get no protection
Contrast this with the 1 gauss, 1 pd setup:
No damage, all ships get 2.5 gauss protection
1 ship loses active, all ships get 2.5 gauss protection
both ships lose active, all ships get .5 gauss protection
1 ship loses fire control, it gets .5 gauss the other gets 1.5
both ships lose fire control, both get .5 gauss
So we see that, until both ships lose their electronics, double gauss is strictly better. In larger fleets, the gauss advantage only grows. This is even more true if your ships have redundant fire controls (i.e. beam ships that can repurpose offensive controls, even at reduced effectiveness), since all ships have to lose their active sensors before that matters at all.
Finally, in the scenario where all of your ships have lost electronics...half a gauss cannon is not going to save you. But an extra 1.5 gauss cannons might have prevented you from getting in this position in the first place.