There will probably be a few Wii games that will shoot up in price, but it won't be like the Gamecube. Gamecube games shot up in price because of supply and demand. Every Gamecube game can be played on the Wii. The Wii was a lot more popular system than the Gamecube. It's the Wii's popularity that caused Gamecube games to skyrocket in price. That is about 100m customers who are looking for old Gamecube games that are not being made anymore.
I think it really depends on the game. Super Mario Galaxy has over 10 million units floating around in the wild vs Sunshine's 5 million. So I don't expect Galaxy to go up in price by much more. Zack and Wiki though? That game took 26 months just to sell 120,000 copies. I'm shocked it's not worth more now.
No More Heroes is another series that I expect to go up in price. In fact it already has in the past few years. I remember when you could get NMH2 for $40. Once the fourth NMH game comes out this should shoot way up in price.
And then there's Little King's Story. Another hidden gem that sold poorly.
Anyway I agree that Wii game prices probably won't climb as high as GC prices did. But IMO this is definitely the bottom of the Wii price curve.
Cripes is GC doing the same thing? I have a nice size collection and with the exception of Twin Snakes and Ikaruga didn't think anything would be abnormally valuable. I think it's crazy what retro is doing and if I was ready to sell any of my games I'd rake in a ton.
Not sure Wii had the kind of stuff that would become rare. Outside of the first party games there was a LOT of third party fluff that rushed in because of how well the hardware sold. Chances are that's all you'll find now. Everyone keeps the first party games. Even then you're right. Now's the time to buy any leftovers for Wii/PS2/PS3 because they're cheap. Can't say they'll go up in value, one can hope though. Do like I do and buy because you want to play. If they go up then cool. Gaming is tricky in terms of investment. They're only worth what someone is willing to pay.
I think a lot of PS2 games will just always be cheap. https://www.pricecharting.com/console/playstation-2 The graph on this page shows price barely moving. The bottom of the PS2 price curve was around 2013. Prices have steadily increased since then, but it's been a slow crawl compared to pretty much any other system.