Having repaired a good few hundred guitars and other instruments, I believe the bridge pin material is of little acoustic importance but of considerable aesthetic value. I would never dream of putting cheapo plastic bridge pins on a good guitar. Aesthetically, I prefer wooden pins, which I have in many varieties - ebony, rosewood and others, with and without abalone or pearl inlay and always ask the customer what they would prefer. I find brass pins rather tacky looking anf fossilised ivory far too expensive. But, at the end of the day I think, as with anything else it's down to personal preference.

I owned a Japanese Lowden like Willie-O's for 14 years (have just sold it) without bridge pins. Excellent sound. My Lakewood has (wooden) bridge pins. Sound also excellent. As others have said the nut and saddle material is of more importance acoustically and I spend a lot of time on both when doing set ups. Personally I don't like zero frets either from an acoustic or aesthetic point of view and think it's just a cop out from preparing the nut properly. I hate to see a very expensive instrument with a zero fret. Again...just my personal point of view from 25 years of working with instruments!

Best regards and peace to all,

mooman