Again, yes, that is the point. As a rule, human beings value rare things more than common things. An object that's the only one of its kind, was used just once, and hasn't been taken out of its case in 48 years is just the sort of thing that collectors would consider extra-valuable, and it's naturally going to score higher bids at an auction than a more commonplace object that was used frequently.
I see what you're saying... in this case, the prop is uniquely preserved and even comes in it's own case, complete with documentation. None of the other props were preserved or documented as well. I appreciate that elevating the value. I guess the rest of it comes down to how much one appreciates the prop itself. It doesn't come across nearly as well liked as the type II phaser. But, there are people who practically adore the phaser rifle... all you need is two people who feel the same way with an abundance of cash and you've got a bid war.
The prop is nicely detailed too, with aspects you'd never notice during the filming. Like how the 3 pre-fire chambers (ribbed tubes) have color coded retaining rings and that there are matching color indicators on a side panel to suggest either status indicators or controls for each (perhaps 3 levels, depending upon how many of the pre-fire chambers you engage). Also, the rotating handle is an interesting idea, serving dual duty as carry handle and shoulder stock. The only glaring thing is the lack of a trigger guard or obvious safety switch.