Because these aren't commodity products, nor are they appliances that eventually become obsolete. You can't value them the same way you value a carton of eggs, or a pair of pants. They're valued more like the way you'd value a painting or a house.
there are only X number of a particular PCB in existence, there will never be anymore of that game made, it doesn't have a limited number of plays before it's "used up', nor will there ever be a "new model" of that game that unequivocally obsoletes the old ones.
It's simple supply and demand, the supply is fixed and it can only ever go down from where it is, meanwhile the demand is subject to the whims of collectors, as more people enter the hobby and learn about the game more people wish to own it and therefore the value goes up because it takes more money to convince those who own those games to sell them.
If you compare that to say a carton of eggs or a pair of pants, the supply is constantly replenished and can be increased rather easily to meet whatever the current demand is. Prices don't ever really increase beyond the cost to "manufacture" and the value of currency.
On the other side of that you have things like (original) paintings or houses. There there only ever be 1 original of any given painting and land is finite so while new paintings can be painted and new homes can be built (just like new games can be created) they don't ever really replace the ones that exist currently. So supply is fixed and demand is based entirely on how desirable they are to the people buying them. And like arcade boards the price will increase until you reach a point where someone who owns one is willing to sell it at that price.
There is a saying that "things are only worth what someone is willing to pay" and this goes back to the idea of "comps" or similar items that have sold recently as a means to determine a used item's value. Because it's evidence of what someone was willing to pay for said item.
This works to devalue items as well. When these games first leave the arcades their value is at the lowest because their supply is very high but the demand is very low. At that time people were bored of the games, they weren't making money in the arcades and since very few people wanted them and there were a lot available the price went DOWN. Now that supply has become lower and interest has increased the price is going back up... it's basic economics.
People who don't want to over pay understand that if they're buying at a price lower than others that have sold recently they're getting a good value; it means that if they re-sell they'll get more than they paid.
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from sales subforums, and then did a search for each title on shmups to get more data.
