Guten Tag, Ewert!
I think that plastic bridge pins are not good enough for a guitar like an Avalon. That is why Avalon puts ebony pins on its guitars. If you try bone, tusq, mammoth, brass etc I think you will get a slightly "different" sound to ebony, but it may not be "better" than what you have now.
IMHO trying different bridge pins is a very expensive way of making a small change to your guitar's sound.
I would say change your strings often, make sure the guitar is properly set up and work on your technique so you are picking and strumming properly.