I began my Trans-Newtonian game in 2050, and it's now 2087. So I'm 37 years in.
The fire control modules are already 200 tons each, and bumping up the tracking speed would've added 100 tons to that. A tracking speed of 12k km/s is only really useful against Star Swarm "warriors", and perhaps missiles in a pinch. But that advantage, in the Rheinland's case, would've come at an unreasonable cost: I'd have to either remove an FCS (and therefore restrict all railguns to a single target at a time) or strip 200 tons worth of other carefully considered equipment.
As for damage control, to be honest I don't really know how the mechanics of that would work in the heat of battle. I have no experience with those modules...
And yes, Gauss turrets are generally the best anti-missile option. However, I mount those on specialized vessels like the Sussex or the hypothetical fast corvette class since they're huge given the maximization of tracking speed and barrels. That said, I have just done a test, and a single-barrelled Gauss turret and its dedicated fire control would weigh 750 tons. That's almost exactly the weight of two CIWS platforms, and the cruisers would be able to defend each other: that means there would be eight turrets firing together at enemy salvos. Hmm. Something to consider, at least for future designs or potential refits.