Zincat
There's no point in mixing gauss and ciws. If you already have the radar and fire control for gauss turrets, just use gauss turrets, because in case you run even just two carriers together, they are SO much better. CIWS are only for when you 10000000% sure that ship will always go solo, and/or when design space is so limited that you don't want to deal with having sensors.
sneer
lots of ciws ( unless carrier operates alone which I doubt ) gauss turret have better value added asa they cover whole TF
CIWS has a sensor built in. 2x CIWS on a ship is a bit tonnage consuming, but also very useful. I use anywhere from 1-8 CIWS depending on what I'm designing and what doctrine I'm beholden to, although I don't always use them.
In VB6, that advice held true, but in C# CIWS is much more powerful overall.
Salvo Changes:
http://aurora2.pentarch.org/index.php?topic=8495.msg115853#msg115853
Point Defense Changes:
http://aurora2.pentarch.org/index.php?topic=8495.msg107268#msg107268
Now having even one CIWS on just some of your ships will make the PD of every ship in the group more effective, due to them being resolved first. In VB6 you needed more B-FCS to engage more salvos, so to defend two ships against two salvos with CIWS you needed two CIWS per ship, but with two B-FCS and two Gauss Turrets on one ship you could defend a whole fleet from two salvos for roughly the same mass on account of the mutual fire. That's no longer true under the new model, now one B-FCS and two Gauss Turrets can defend a fleet from two salvos, but with two CIWS any ship can defend itself from two salvos for roughly 50% less mass because it saves weight on Fire Control. So in C# CIWS is now more cost-effective for defending a ship from missiles than Gauss Turrets are. They're also more accurate than Gauss per ton overall.
Sorry, I disagree for any kind of fleet situation.
The enemy will still tend to target all your ships at the same time. So most of the ciws of the fleet will be doing absolutely nothing. As such, the salvo changes don't even matter in this specific case.
Say you have 10 ships. And you allocate 1200 tons for PD on every ship, just to simplify. I don't have the game open now, so I'll just make a very rough example. And you have incoming missiles.
If you put with 600 tons in ciws and 500 tons in gauss cannons+ 100 tons in BFC on each, the targeted ship will only be defended by 600 tons of CIWS and 5000 tons of gauss.
If you had done 100 tons in BFC and 1100 tons in gauss cannons on each ship instead, the targeted ship will be defended by 11000 tons of gauss. No matter what your targeted ship, I'd rather have 11000 tons of gauss defending it. And the bigger the fleet, the more this is true, because more and more CIWS end up being unused and you could have put gauss cannons instead.
You might say: but I had some space, so I snuck in a CIWS. I'll counter: but you might have reduced the fuel storage by 100 tons (for the BFC) and used the gauss cannon instead. The cost effectiveness (assuming you mean construction cost) is also.. dubious. If you build a fleet, it's not that very small cost difference that will actually matter.
I am talking about normal situations. If you have in mind a human player who changes the salvos to play around the mechanics, that's a different matter. I doubt it would matter all that much though, and honestly I don't even care since I don't play like that anyway
And I do use CIWS on important ships. But that's for RP, since I'm an RP guy to the heart.