For me, what makes a pen, or an expensive pen rather, worth it cannot be attributed to any single factor.
I like gold. I'm weird that way. I agree unreservedly that a steel nib can be just as smooth a writer as a gold nib when properly tuned, but I like the look of the material, and gold nibs offer a slightly different kind of springiness to the writing experience that cannot be easily emulated by steel nibs. I'm not saying all gold nibs are springy, since there are a few 21k nibs (cough cough) that are fairly rigid nails as well, but that gold nibs are usually softer and more pleasant to use is a statement I think true enough to warrant a casual generalisation.
Another factor is aesthetics. Some pens look great with a bare minimum of bling, like the Lamy 2000 (though some dislike its design, for whatever reason), while others, such as the Pelikan Toledo pens, utilise fairly pricey components that add a more complex, more ornate design to the pen. Busier designs aren't for everyone, but for those that enjoy them, then I suppose they can justify price premiums by means of all the extra stuff on the pen.
I suppose one of the bigger contributors to a pen's price that makes it "worth it" is the amount of effort that goes into actually making these pens. Fountain pens that roll off an assembly line will usually be cheaper than ones that are handcrafted, which explains the price of Edison Pens' Signature Line offerings; machines can get by well enough without a salary, as far as I'm aware, but people do need something to help pay bills with
Brand recognition might also play a factor, since as in the case of Montblanc pens, well, the brand is commonly associated with a certain level of prestige, and some would say that it was a privilege to own a product of theirs; while not everyone thinks that way, it's still something that an individual may feel makes an expensive pen "worth it".
Now, the above are merely what I consider to be the things that make an expensive pen a worthwhile purchase for the end consumer, If we were to talk about what makes these pens expensive, well, I'm sure that a lot of that would be companies trying to make back what they spent on marketing.
I just read Keyless Works's post after submitting mine, and remembered that I recently got my first vintage pen, haha. Yeah, in those cases, the scarcity of the object definitely plays a role in determining its price, and its worth to the buyer. The condition of the object is also something that one would take into consideration, since it only stands to reason that objects of advanced age in good to mint condition, rare as those are, would be in greater demand, and fetch a higher asking price.
Edited by Lyander0012, 07 August 2014 - 04:48.