If the noid is not lighting at times... then it is not getting the signal. I do not know how a noid can flash when the wire is essentially pulled to ground.. .but it will flash OFF which is when the coil & plug fire, so it will flash.
Anyway, no flash means no change in voltage. Two causes, I think, conduction and the actual change of the V present on that pin in the ECM. Could be what has been suggested, a bad connection to the ECM.
Have you taken the 3 large connectors free of the ECM, right there sticking out of the plenum at the base of the windshield? The box that is supposed to prevent water intrusion can allow leakage, and the connectors are not perfect, and could have some corrosion.
Just as a thought, the drivers for the spark plugs generally will not FAIL and then WORK, they are either open or shorted when they fail. Having an intermittent points more towards breaking contact, such as a bad pin/socket or a bad solder joint on the circuit board.
The rubber boots on the COPs will mostly fail and get worse with time, and finally the plug will get nothing as it all will take the shortcut. From here, I do not know the frequency of the misfire, but went back to one of the earlier posts and got the impression, from the noid' post, that you have intermittent, and is is really intermittent, but more noticeable at idle rpms. Thus the ECM/pin/board comment.
added.. FWIW, you could be having misfire at higher rpms but because they are hidden among the much higher count/minute, they become indetectable to human senses.