Who really cares, i personally do not. whether it is "precious resin" or Plastic it would not make a difference to me.
First off, lets get one thing straight, Montblanc is by no means the most expensive pens made. Montblanc is just the most well known luxury pen company in the world.
I personally by my pens because i like the way they look or the way they write. if the happen to cost more or less than another pen, it would not matter. i by what i personally like.
Personally i would not but the Iconic Montblanc 149 Fountain pen, not because it is made with the "precious resin" but because it is boring looking. But my Montblanc Tolstoy fountain pen is a beautiful pen (to me) and i think it was a steal for what i pay for it. Yes it has Plastic on it but it is constructed 1000 times better than any plastic bic i have ever bought.
So again i say, WHO CARES.