I have historically used either color preserver or rod varnish on my wraps even if using an NCP type thread in order to essentially fill in the air gaps within the thread and help seal it. In my mind at least, this helps to minimize air bubbles escaping when applying the epoxy. Is this a reasonable practice or an unnecessary waste of time?

I think it is unnecessary.
Norm

Ernie,
I also consider it unnecessary. When one thinks about it, they are all accomplishing the same thing, saturating the thread. Generally, the thinner the viscosity of the material = the easier, quicker it will be absorbed into (or at least around) the fibers through capillary action. The tunnels along the sides of the guide feet require special attention as the large void can be “sealed-off” making it difficult for the air to escape and be replaced with epoxy, CP or whatever. Rather than coating the entire guide wrap at once, especially the open ends of the tunnels, apply the epoxy to the first third of the wrap to allow it to fill the tunnel around the toe of the foot, then the next third allowing more of the tunnel to be filled, and then the final third to completely fill the tunnel. Does it take more time? A bit. Is it better? I think so.

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Not needed, extra time and step that is unnecessary.