I'm pretty sure point (a) is false [1], and I'm absolutely sure that the conclusion (trust the Googlebot!) is. You should probably optimize for humans first, but not humans only. That's just not the way the web works.
http://www.seomoz.org/article/search-ranking-factors
EDIT: I realize the SEOMoz data is based on SEO experts ranking what they believe is most influential, but what else are you going to go on? Maybe patio11 or someone else on here who is an SEO whiz can offer some of their experience.