Not a lot to add but as a "acoustic guy" I feel obliged to jump in.

Like wingsdad I replaced a nut on a old Guild. In my case the mid 70's D35 in my sig. Replaced it with Tusq and it made a big difference. Much better mid range, bit of a improvement in the bass and better volume. But, the existing nut had been messed with. On my Martin D2R the previous owner had goofed the saddle up. I called Martin and they sent me (no charge) the spec micarta saddle. Again a big difference.

My experience is replacing even a good fitting plastic saddle with proper bone or Tusq will be an improvement. Bridge pins and nuts less so.

A interesting test is to drop a plastic saddle or bridge pin on a hard table top, then do the same with Tusq or bone. Plastic will make a thawp kind of sound, the Tusq or bone will ping like a bell. Gives you a sense of the sonic difference.