I have ebony pins in my Yamaha, and I honestly can't say whether they changed the sound noticably. I did it for appearance, and the fact that I hate the standard little plastic pins.
I have my Alvarez 12-string in the hospital right now, getting the Fishburn Matrix Natural preamp/pickup system installed, and Stephen is getting me a set (2 actually) of brass pins to replace the previously noted plastics. I can't wait to hear it, but I may change to ebony pins if it's too bright...the 12 string already shimmers as it is...

rugburn®