I'm an Animal Crossing super-fan and am wondering if you know why the Not For Resale relay cartridge has gone down in price so sharply from a few years ago? I'm only asking because I remember that I had an extra many years ago and sold it for over $200 and if I remember correctly, others were asking up to $300 for it. I'm really happy I decided to sell my extra back then but I also had a few of the Nintendogs relay carts that didn't seem to bring much many years ago but have seem to gone the opposite way and have gained value.
I guess you just never know with games, the usual thinking is the older it gets, the more it will probably be worth but not a great rule to go by.
I'm also a huge Atari 7800 collector and since I started a decade ago, I've seen a huge amount of sealed games hit the market since then. I believe people have crazy good warehouse finds or something and usually flood the market which makes games that were rare, now easily found and at an increasingly lower price. The 7800 seems to have calmed down and even on the rise now but I believe people somehow find New Old Stock that's been in boxes somewhere for decades. I have the entire collection now but it wasn't easy....or cheap!
Good luck with your trades, you have some awesome NFR carts there. I collect DS too and was into the NFR scene for a year or so but it just got so expensive. I managed to hold on to one Animal Crossing Relay cart though. I scene at least 2 go for $25 a couple months ago on ebay. Now, a seller has "More Than 10 Available" for $50 each and I believe he's a member here that I dealt with many years ago - retrogamer or something like that - he was a cool guy!