Coincidentally I was just watching a few documentaries that dealt with these online gaming economies, and I do find it to be fascinating. I'm not a gamer, so it boggles my mind that people would pay so much money for what amount to cosmetics (if I'm not mistaken). My mind shouldn't be boggled, however. I've seen people go crazy for weirder things than CS:GO skins in the course of my lifetime.
Yeah, wouldn't dream of spending so much money on an virtual item, either. But when you see that there were people paying thousands of dollars for other online items / collectibles, I stopped beeing surprised about what people spend their money for.
Not only that but every other risk associated with centralized/monopolized market applies here as well. Valve could go bankrupt, get hacked, shut their servers down for any number of reasons, become greedy and implement "property taxes" in addition to the commission. On the other hand, if they were truly benevolent they could find a way to "migrate" those items into a new version of the game if it comes to that. Regardless, investing into something that 100% depends on one company's whim sounds like an extremely bad idea. Obviously a lot of people don't think so.
I wouldn't see it as a classical kind of investment anyway. More like some kind of gambling money with high risk but a high potential reward. Fact is, that stickers from previous tournaments would've all left you with more than your initial investment. So I'll probably try my luck and spend a few hundred dollars on these limited stickers when the next tournament is around the corner. Then forget about the game again and be surprised when checking the prices later on. One way or the other ...
Right now I am just not sure if the current prices are caused by the popularity of the game itself and by players who buy skins to play with or if the price is driven by people who only see it as an investment.