hmm, I can't speak for others but for me. when I make a decision to invest in a rare I use a combination of the following reasons and the weight in each of these reasons changes depending on how much each factor influences my overall desirability for the item:
1. Quantity - this would be true in the case of your item.
2. Functionality - is the item wearable, wield-able, decorative?
3. Name - does the name sound appealing?
4. Graphic - is this a graphic not often seen in the game?
5. Hue - is it something anyone can make from the various dyes out there or is this a special hue
6. Invest-ability - is this something that can be resold later? It doesn't mean it will ever be sold but the thought that it could is actually a reason for some people to collect.
7. Experience with the market. This sort of ties in with #6 but the difference is that if this factor was used then the item most likely will be re-sold down the road if purchased. In your case, the opposite had happened, i.e. asking for a price check and gotten little interests from it. So sometimes asking a public price check can be a double edged sword.
8. Desirability - for some people, owning something that other desires is in itself a reason to collect.
While collectors may consciously or unconsciously uses some or all of these factors when deciding on whether or not to buy an item, there is always the X factor, i.e. someone out there has been dreaming of owning a 1 gp white check since the dawn of time and will pay you 100 mil for it so that "factor" can never be ruled out. But usually when a week goes by and still not a positive response or PM from anyone pretty much tells you that the item was meant for you to collect only and no one else.