I'm pretty sure you'd be crazy to value the time and energy you spend on these activities at only $8/hour.

Another way of thinking the cards would be "if it takes me 30-40 seconds to memorize this card for 3 years, how many seconds do I expect to spend looking up the information on this card if I don't bother to memorize it?" Would you really spend 30-40 seconds looking up information on the median card you'd consider memorizing?

As for dual-n-back, first there's the critique you mention in your FAQ, which seems very damning. Second it's quite unpleasant in my experience at least, and therefore uses up a lot of energy. And third, I'm inherently skeptical that simple mental activities like dual-n-back and nintendo brain age could increase your IQ faster than complex activities like writing software that someone might be willing to pay for or becoming proficient in economics--and these last activities have significant side benefits above and beyond possible IQ increase.

If you just want to increase your income I suspect there are much more efficient and direct ways of doing it. I have a few arbitrage-type ideas I can share via private message with anyone who expresses a desire to donate a lot of their income to preventing human existential risk.

For what it's worth, when I first wrote this post many months ago, I thought time spent on pure self-improvement activities was generally time well spent. Now I think it's generally not time well spent unless you're at the point where you spend eight hours a day browsing reddit or something like that. My view is that if you're able to spend a decent chunk of the day working on worthwhile projects, you should do that, and your self-improvement efforts should be limited to running day-long or week-long self-experiments on yourself that don't cost you many productive hours and recording the results of those. (Example of such a self-experiment: if you're a programmer, write down every bug you have, estimate how long it takes to solve, and once it's solved record how long it actually took to solve and the details of your solution. Then periodically review for trends. I've done a little bit of this; it was highly unpleasant/boring but it seems intuitively like it could be quite beneficial so I'm planning to do it more.)