I remember about 20 years ago, we were selling Guild's import line, Madeira Guitars. We received 2 models in one shipment. The cheaper one had wood pins and sounded better than the more expensive model. We swapped pins in the 2 guitars. What do you think happened? The sound went with the wood pins to the higher priced ax. Ever since that day we stick wood pins into factory guitars like Martins and Guilds with pleasing results in the resonance and sustain. We like to take a Martin sold by another dealer and get the owner to try a set of ebony or rosewood pins. After the player hears the improvement they will generally ask our advice on other upgrades that can be made to their instrument. Plastic is useful stuff because it absorbs energy. Not too useful in the "engine" area of your guitar where you want as much organic vibration as you can get. Think of plastic pins, bridge saddles and nuts as shock absorbers. Good results come with cow bone, walrus ivory and "fossilized" ivory. Brass sounds pretty metallic for my taste. We just tried some new samples from Tusq. They have improved, but their main advantage seems to be predictable factory shape, the one-size-fits-all concept.