Check the fusible links at the battery if you haven't already. I actually just had one fail the other day. My gauges were dead, no power to windows or stereo, etc. It did it intermittently while driving then was back to being fine, a few minutes later after I parked everything died. Still cranked over and fired but there are a few different fusible links that go to different things. Quick and easy check.
When the CAS goes bad it's usually instantaneous and they don't ever work again. They just fail.
Also, the tach is wired to the coil transistor via a white wire so it could very well be coil related. I see you already did some fixin.' A rubbing coil wire in my Pathfinder last year did all kinds of cool stuff, and only at night at the right angle could you see it grounding out.