I think prices are stabilizing. Demand for some games has dropped, and therefore the price has dropped, but that does not necessarily mean the whole market is trending downward. Some systems are trending slightly downward like nes and snes, but Gen 5 and Gen 6 are going to continue to trend up the next few years.
https://www.pricecharting.com/
Check out the prices for Saturn, PS1, Dreamcast, and PS2, they are dropping pretty bad overall, as are many other systems. Retro Nintendo prices have been leveling out on average, however there has been a noticeable drop in price on the more common, yet sought after games. This matches up with ebay and what is happening in the community in general.
I've looked at a lot of the charts on pricecharting and gamevaluenow and I'm just not seeing the same doom and gloom yet. Top value games on the Saturn, PS1, PS2 are continuing to climb in price for the most part. Some valuable games have become less valuable and are then replaced by other games. I just think the retro market is too big and diverse to say that it's in an overall decline. 2017 may have very well been a peak for many systems but we are only one year removed, we won't know for at least a few years what is actually going on. I would actually welcome a decline but it just feels like wishful thinking at this point.
There are always going to be games that go up in value or stay valuable. Hell, there are some gen 2 games that have stayed really expensive since collecting for was in its prime in the early and mid 2000s. But just because a minority of games are going up or are retaining their value doesn't negate the fact that the majority of the library is losing value due to decreased interest. I am under no illusion that Little Samson or Panzer Dragoon Saga will be $20 games someday, but I am confident that a game like Contra or Castlevania 4 will be around $10 again. These common and even uncommon sought after games have already declined between 20 and 40% in the last couple years and I believe this will be a trend that will continue slowly for a while. That's not even mentioning the hoards of shovelware and mediocre titles that have risen in value for one reason or another, but recently have dropped sharply since the desire to have games like this is becoming less appealing to most collectors.
Price Charting is not gospel when it comes to averages prices on specific games, in fact I never use them for that. But they do a decent job of capturing what's going on with the overall values for games which seems to be reflected by my own subjective experience of seeing games go for cheaper online, retro game stores holding onto inventory way longer than they used to, collectors and resellers leaving the hobby in greater numbers, and a zeitgeist within retro gaming that the glory days of peak retro prices are behind us.
It is far from wishful thinking, it's happening as we speak. Sure, we may be several years away from bottomed out prices across most retro platforms, and I don't think there will ever be a time where there is nobody that wants these games. However, I do see a time when retro games are not as desired and sought after as they have been for the last 5-years, and most collectors (and resellers) have moved on with their lives. Again, this is already happening if you combine the data with subjective accounts that seem to be fairly consistent on here.
