Might as well add that most of these games have been out between 20-10yrs now and their physical value has been settling over that time. The general demand for the title is what drives its price and the rarity in some cases, but popularity is always #1 in price driving. If suddenly everyone hates classic gaming then there'll be a huge crash and a flooded cheap market, which I'd doubt you guys will do that. Because, once again they have been out 10-20yrs, most of us that grew up to these classics can now afford them living out of the parents house and what have you, but in another 20+ years the next generation or 2 of people won't have the exposure to the now classics and the demand will drop causing that crash in these games. So it's not a matter of system releases that kill prices, it's the generation of users/gamers that ignore or don't demand these other games and systems. So one day you may see all but a few elite games going for $1, and those highly still über rare protos and all still going for a few hundred due to collectors value.
Not sure if I said all that in the right way, but I'm sure most hardcore collectors already know this rule of thumb for supply/damand pricing and all. So time will drive game prices, not new generations of gaming.