Yes, there appears to be good evidence that Vitamin C and Zinc aid immune function. Yes, Iodine deficiency is real, and you should ensure you have enough. Yes, 5-HTP, Tryptophan, Melatonin, and Magnesium are excellent sleep aids. Yes, Caprylic acid oxidizes in the gut to produce ketones. Optimizing bodily function starts with diet, continues with exercise, and finishes with topping off whatever is missing, or reducing whatever is in excess. Knowing what's in your food, how your body interacts with it, and how to supplement it doesn't seem like hand-waving to me. The hand-waving comes when people make extraordinary claims far exceeding the known effects of any one of these tools, and with time and effort, it is possible to cut the wheat from the chaff.

There really is nowhere near enough epidemiological study on the effects of nootropics or performance enhancing drugs, in general. Much of the science surrounding the recent wave of biohacking is bleeding edge and, often, a study on some particular use also represents the entire corpus on its effects. In service of biohacking, this makes it difficult to weed out the hacks. As ever, caveat emptor.

That said, when it comes to making personal decisions about what helps you or hinders you, I don't believe you necessarily need to be a neurologist or an organic chemist. You can collect stories from other people, and take them on balance with what studies you can find. Going over something like http://www.jbc.org/content/89/2/547.full.pdf won't make for exciting reading, but it can help you make informed decisions. You can, with a cautious and self-critical attitude, guinea pig yourself, taking logs and noting your overall health and performance, preferably with the help of your doctor. You can ask others near you if they notice any changes in your performance or mood. And at all times, you can ask yourself how you feel.

There are a lot of people cashing in on "brain drugs" of late. You mention Bulletproof (Dave Asprey), and while Dave surely is making good money, he does sell decent products. To be considered separately, Dave openly advocates for sourcing food and supplements from wherever they may be cheapest and of good quality, but I happen to like his coffee, so I fork over the cash.

I don't know how placebo effect for one supplement could amount to much if you're already taking 30-40 vitamins, powders, and capsules a day (as I am). If I take one more white gel cap, I barely notice. What matters to me are my notes over the last few weeks, whether I've observed any positive or negative impact in that time, and whether that impact was sustained without any obvious confounding factors. This is hardly a multi-year, double-blind trial, but it is enough for me to confidently decide whether I find a drug's results favorable enough to continue using it.

As a freelance contractor, falling into even short bouts of illness, depression, indecision, immobility, or myopia represents a real and ever-present threat to my quality of life. For me, $1200 is completely worth the price of finding new ways to increase my total productive time. For others, that money is better spent elsewhere. Yet I would argue that even webmaven's purchase of a good chair and keyboard is right up there in my original list, under "whatever I find works." Any investment in one's health, I believe, is sure to be repaid in full, for what use is the rest if we do not have our health?