Surely the market value of these will only hold up as long as they're within the normal lifespan of the people for whom the original NES is a nostalgia item?
For example: If you were born in 1978 and were 7 to 8 years old when your parents bought the original NES and brought it home with a small selection of games, that's probably a core memory for you. And probably exactly the same demographic now who will pay big money for these things.
But as this generation of people ages, do people who have no childhood memory of a NES (or SNES, or Genesis, etc) because they were born in 1999 consider these things to have any value? Will their value drop significantly when there's no longer a population of age-range-appropriate nostalgic collectors to buy them?
If these are being treated as some kind of "how many dollars per unit" valuable commodity to be traded/hoarded, is it the best possible solution to convert a collection of something like this into currency before the collectors age out of the market?