"Zero frets/fretboard wood/massive bridges/body wood make a practical, discernable difference to the sound of an electric guitar or bass in a modern rock or pop song"
I'll take this one, it's easy. Massive bridges can make a BIG difference in the way an electric guitar or bass will sound. That other stuff can be "iffy", I've tried out quite a few Les Pauls that were heavy but sounded like a wet log. Wood varies, if it rings it absorbs energy from the strings.
Whether anybody/everybody/nobody can discern the difference - that would require testing.
I can say with certainty that the many times I've installed a heavier, more massive bridge the instrument had a more even response and much longer sustain. It is possible in my experience to immediately notice extra clarity, eveness and sustain.
That might not be noticed in terms of the tone - depending the signal path at the recording and all production after that, but it could inspire the musician to play differently.
I have some guitars/basses with stout hardware, even the mass and mounting of the tuners will change the tone of some guitars. The length of the string path behind the bridge changes the tone, so does not having any - wraparound bridge like Les Paul Jr.
The effect of the mass is to dampen the resonance that robs strings of energy. Think of the difference between a banjo and a Les Paul. That's an exaggeration, this is a much smaller increment of change but I vote yes.