Note: I just noticed that your cards are a little different than the ones in the link that I discuss below. I doubt if that makes much or any difference in the numbers. I think all these type items are made the same. I've never seen one that was electroplated. Even if it were plated, the plating would be quite thin. No need to plate it thick. It wouldn't look any different. According to eBay, yours originally sold for about $10 each.
I have some experience with real gold embossing foil (what they used on those cards) and a lot of experience using real gold leaf. I feel very confident that the embossing foil is made by loosely adhering gold leaf to a paper backing. 22K and 23K are common gold leaf purities. It is applied to the card, using a 3D embossing die, by pressure and maybe some heat. The paper is then peeled off. I don't know if they still do it but, when you bought a new CRC Handbook, they included a piece of paper with gold embossing foil on one side. On the cover, there was a rectangular area. You put the paper, foil side down, in this area and wrote your name on it. Your name was then displayed on the cover in gold. It lasted an amazingly long time.
Gold leaf thickness, no matter what karat, averages about 3.5 microinches (.0000035"). The value of 3.5 microinch thick gold, at today's spot, is about 6.3 cents per square inch. Assuming the area on those cards (2.5" x 3.5") covered (about 90% coverage) by gold to be about 8 in2, the estimated gold metal value per card would be about $.50. To buy gold leaf, you pay about double the gold value. Since embossing foil requires more manufacturing steps, the card manufacturer maybe pays about triple the gold value or, $1.50 per card. On the link, the cards retail for $12.95. Considering material costs, manufacturing costs, marketing costs, salaries, profit, gold waste, rejects, and other overhead, the $.50 of actual gold value per card sounds right in line to me and maybe even a little high. Your 50 cards are worth a total of about $25, and probably less, in gold. I certainly can't see them being worth more than this.
On the other hand, as a product, 50 cards retail for $647.50. Don't you think it would be smarter to try and sell them as cards, even if you only got $2-$4 each? Recovering what little gold is there could be a terribly disappointing (and difficult) experience. If my math is right, $25 worth of gold would make a cube a little smaller than 1/8" on a side.
With gold. novices tend to think they have a fortune without logically examining the facts. When the material is yours, it's natural to get the idea in your head that your material is worth a lot more than it actually is. I am occasionally guilty of this, somewhat. The apparent value of these cards is very misleading to the average person and that is why they sell a lot of them. The buyer sees this large area covered with beautiful rich looking gold and automatically thinks they're valuable. They don't know that thin gold usually looks exactly like thick gold and that the value is totally dependent on the thickness (and the area covered, of course). They don't know that a manufacturer of anything will never, ever intentionally use more gold than is needed to meet their ends. With electronic parts that might experience wear, they need (and use) about 30 microinches of gold. With these cards, all they need is good coverage and a rich shiny gold color. For that, 3.5 microinches of gold leaf is completely adequate. Unless they are rare and have an added-on collector's value, they are a sucker deal for anyone that buys them at $12.95.
Some readers may question why 3.5 micro" of gold leaf is a rich gold color and 3-4 micro" of plated gold looks very pale. The reason is that the average density of plated gold is always less than that of cast gold. When you start plating an object, the plating is quite porous and the density of the gold is quite low, maybe only half of that of cast gold. As it gets thicker, the pores start to fill in on or near the surface and, at about 100 micro" (depending on the type of gold bath used, though), the pores are almost totally sealed, at least on the surface. The pores below the surface never really fill completely because most all types of plating don't "throw" well, especially into blind holes.
On the other hand, gold leaf is made by hammering cast gold very thin. Its density is very close to those values found in the books for that particular alloy.