There are two problems with self-investment. First, there's coupling or frictional losses, by which I mean that X amount of money invested in yourself does not directly translate to X*(1+epsilon) money next year, even probabilistically. You have to put in work. Money invested in the stock market doesn't go through a stage in which you use your new skill; it remains, as it were, money all through the period, so there's no loss from transforming from one form of capital to another. Second, the proposed purpose was to free yourself from having to work, through accumulating capital. Although we call the result of self-investment "human capital", it doesn't have the fire-and-forget property of traditional capital; you can't use it with other people's labour.
I agree that this is a significantly different proposal than the original idea. It's a combination of the original idea with another idea in a munchkin-like fashion with a different result, but one that is potentially better/more powerful/has higher XP (though it's not guaranteed, of course). I wouldn't call your points problems though, just differences.
By the way, there are ways of getting yourself to put in the necessary work (i.e., overcoming akrasia), and this community is great at coming up with a lot of them. Do you think that if you had $10,000 (to ...
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.