As for prominent people using nootropics:
Astronauts on the ISS use Modafinil and Melatonin. https://en.wikipedia.org/wiki/Space_medicine
There's some indication that President Obama might be using Modafinil, but the evidence is a little thin. http://www.thedailybeast.com/articles/2010/03/04/the-white-h...
Dave Asprey, from the bulletproof executive uses Modafinil. https://www.bulletproofexec.com/why-you-are-suffering-from-a...
Tim Ferris from the four hour workweek uses racetams/choline. (Can dig up a source if you're interested)
Soylent's new Coffiest contains the classic Caffeine+L-Theanine combination.
Peter Thiel takes human growth hormone — although more for longevity than nootropic effect. http://www.bloomberg.com/news/articles/2014-12-18/investor-p...
As for why not more smart people tout their use: why would they tell the world? There's no value in it to them, and there's a lot of stigma around using "chemicals" when someone isn't ill.