Wow that's a tough sell - you pay $25k for a NIB hugely collector's item ... will you actually ever remove it from the box? Guessing that would drop the value immensely almost immediately. Kinda funny to think someone could buy and just display the box in their game room - saying that "That's a NIB Scared Stiff in there from Elvira! But I can't open it cause it would drop $10k in value!" ..

What if this is the same one?

I think it makes more sense that it may be the same one, since the OP says it "came from", as in it was a prior purchase. I'm sure she could have gotten as many as she wants, but I doubt she just kept them all NIB sitting somewhere all these years.

Ebay auction from 2002 with pics of NIB:
http://robertwinter.com/pinball/ss/ebay/auction.html

Being that his handle is RobertWinter, and it's on the Robert Winter website, I think it's a pretty easy conclusion to come to. So basically looking for $15k profit after a bit over 10 years. Also confirms that if you're going to buy something like this, you're probably keeping it in the box. So buying it as an investment.

NIB regular Scared Stiff would be ... what? $10k? $12k?

Let's say $12k.

The only "extra" this comes with is a signed letterhead certificate of authenticity.

So basically you are paying $13,000 for a signed letterhead. The NIB SS has no real extra value that I see as it has no plaque or anything else making it valuable, and nothing to differentiate it from any other NIB SS. Or am I missing something?

I do agree with this, but there's just not much there. It's different, as in the Ebay auction, if you went over and met them and got them to sign it, etc. I'd think there'd be much more value in that and the signed machine, than in a NIB one with no indications of ownership other than a letter. Which would a collector rather have - a NIB one with no signs of ownership other than a letter, or an HUO one signed personally with a picture, signatures on the machine, and letter? I'm thinking the latter. Usually if you buy something with a story, there are some "cool" unique thing(s) that go along with the story. That's what I think is missing here. The only thing of value is the letter.