For what it's worth:
I have SEVERAL of these types of cards (heck, I was even allowed to emboss my own cards a couple times). I asked Admin about adding them and his response was that we can't list them because there really is no way of knowing what exists, and add to that the fact that there are reports of people (like me) who embossed their own, but switched out the card at the last second and embossed Topps and Upper Deck cards! What I do is I add another copy of the card that is embossed to my collection, then I edit the details on that copy, and enter in the "Comment" field which show it was stamped at. Others cannot see it, but I can, and that's what is important to me.
As far as "value" goes, just like with any other cards, it all depends on who is looking for something like that. If it was a player I collected and from a show I wasn't at, I might go double the card's normal selling price just to have the different card. Not being a player I collect, I don't want it at all, and if I was trying to put a set together and this was a missing card from that set, I would pass on it so I could get a non-embossed copy (to match the rest of my set). So it really does depend on the player and who collects them.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).