[Updated August 2015]
Some time ago, my brother visited me, and saw one of the lucha masks that I have. It was a split Guerrero Maya Jr. / Multifacético mask, a design that Guerrero Maya Jr. uses only when facing Black Terry on independent shows. There aren't that many of these in existence: three, as far as I know, as of August 2015. Mine is signed to my real name by "Guerrero Maya Jr. antes Multifacetico". My brother asked me how much it was worth. I told him that I didn't know and that I was planning on never selling it.
Somewhat more recently, I was told by someone in Mexico, "What gives value [to a mask] as a collection item is the use [by] and signature [of the luchador]" (translated from Spanish and context added by me). I replied at the time that I didn't have a strong preference either way for new or used masks -- which, on the surface, was true: about half of the original masks I have are new, and half were used.
For those unfamiliar with the term, an "original" mask is one that was originally made for the luchador in question, or at the very least by the same mask maker (mascarero) using the exact same design and sizing, rather than by a different mascarero imitating the design. (The emphasis is on the "origin" part of original.) This is a matter separate from materials and construction quality, and separate from "official" masks. (A luchador can authorize a non-original mascarero's products by signing or tagging them.)
Non-original masks are often high-quality in and of themselves. The problem is that, if you value accuracy highly, it's very difficult for the mascarero to make things exactly the same with different proportions and such. And, especially with newer designs, it often takes them a few iterations (i.e., delays) to figure things out.
So the primary attraction for me in original masks is that I know that they will be accurate because the luchador in question has at some point looked at the design. That I can get the luchador to sign them is nice, but secondary to the fidelity of the design itself. If I care enough about the design (or the luchador) to care about the mask, I want the design to be exactly that, and I am willing to pay a premium for it, and am willing to make it worth someone's time.
As for whether a mask is used or not, obviously, when a mask has been used in a specific important or memorable match, that's one thing, but if it's an unremarkable weekday match, I would actually prefer an unused mask by default. I also highly prefer that the mask be intact -- ripping of a mask on a random storyline build kind of destroys the point for me; chances are that I'm not going to remember the middle of a long multi-month build. However, I'm not opposed to a lightly used mask in good condition.
Unless the luchador actually offers a specific used mask, I don't expect to be able to acquire one, though. However, this is something that actually varies among luchadors; some simply assume that, if you're buying a mask from them, you want it used and will use it once before selling it.
In my experience, luchadors generally (although not universally) charge for masks based on their own standing and on the cost of the mask itself, not whether the mask has been used. The person who told me that a used mask is worth more is right in that a used mask automatically has some story behind it. But since the value of original masks for me comes from their inherent accuracy of the design, I have to balance a worn mask against that.
And far more interesting than the stories of how the masks were used are the stories of how one actually comes to acquire them, especially if the luchador hasn't offered them publicly. (Although some do, many luchadors don't explicitly let you know that they have merchandise for sale; it's an unwritten rule of lucha libre culture that most luchadors will sell their merchandise if asked seriously, though. This trend appears to be slowly changing, though, with more guys being open about what they have or partnering with sites like Masked Republic.)
I'm especially grateful for the opportunities that I've had to buy original masks, given that this traditionally [again, Masked Republic excepted] involves a conversation not only
about the mask itself and price, but also the logistics of actually
getting said mask. This is not straightforward when the seller is not
supposed to reveal his real name and is some thousands of miles away. I
always feel as if they have better things to do, and I don't doubt that there are luchadors who would make this experience unpleasant. However, for me, things have generally gone extremely well, and the luchadors with whom I've interacted have been incredibly nice.
And in the end, there is no way to put a value on those stories.
