I did hold a lot of valuable in-game items in several MMORPGs when I'm still in NA. Nowadays, I fancy CS:GO and Dota 2 item betting since it's really fun and takes your profit up there as there are tons of traders, buyers and sellers literally everywhere. I testify to the appreciation of value of some skins on the market, notoriously the Titan Holo Stickers, Emeralds, Rubies and Blue gems and the recently-released AWP | Gungnir which saw a massive boost in price over time. While there really is money to be made in hoarding valuable skins and selling them for later, I still think it really isn't a robust and bulletproof way to trade your way up to riches. Youtubers are making massive money for it because they are already known, and the issue of trust doesn't apply to them, take for example, Anomaly which is a known cheapskate in the trading business. Next, as you've mentioned, you have to be reliant on Valve for not making some foolish moves else your money will go down the drain. There are tons of trade-banned accounts even though they did not participate in a scam but rather bought scammed items, so there's also that.
tl;dr: CS:GO skin hoarding, trading and selling is good for a profit source but not really recommended as a main investment opportunity due to uncontrollable factors imposed by Valve.
Interesting. You sound like you have some experience with the CS:GO market, already. How 'grown' would you consider the skin market? I mean, do you think the curret prices, in particular the ones of stickers from previous tournaments, are backed by real players who buy to apply them on their skins?
You also mentioned that there is the chance to get your Steam account trade-banned? That would kill the whole investment ... How likely do you think is it to get one just by buying cheap cases in the Community market and tournament stickers ingame? If there is real chance getting your account banned at random, that's an absolute no-go and then I wouldn't put a single cent into all of this. I think, I first played the game in 2015 but so far, I had no issues.
As you can see, I don't really have much experience at all. But it's funny, the more I dig into this, the more parallels to crypto are visible. From the hope that the Chinese pump their money into the market to P&D-like schemes where Youtubers suggest their followership the next best skin/item to invest in.