Thanks for the replies.
I replaced just the cables, for what it is worth.
And yes - the rear shifter cable is the one that was frayed at the shifter. Oddly enough, that was the only "bad" cable of the 4 (2x brake, 2x shifter). However, having replaced all 4 that makes me pretty confident in their service.
When I put the new cables in I added TriFlow lube to them. None of the cable runs were sticky. The rear brake was the only one that was stiffer and that is because it is a solid housing all the way to the rear dropout. All the other housings are much much shorter (shifters are only from the bar to the down tube and the rear has the curve at the rear, the front is only the bar to the down tube).
So for now, and until something else comes up in performance issues, I am fine with the new cables only.