Interesting idea. I think a certain amount of rationality is desirable -- people of below median or even near-median rationality go round making really stupid decisions which screw up their lives. On the other hand, once you've stopped hiding from imaginary demons, buying magnetic charm bracelets and drinking venti caramel frappucinos, further effort in becoming more rational may be severely diminishing returns.
How would it really help me if I were more rational and less subject to cognitive biases? I don't think it would help me much in making my day-to-day decisions. I honestly don't think it would help me in my work, either. It might well help in tackling really, really difficult questions where it's extremely difficult to disentangle your own feelings from the correct answers -- things like "What is the probability that humans will one day achieve immortality", or "What is the fairest possible tax system?" But would answering those questions actually enhance my life? Humans will achieve immortality, or not, regardless of whether I correctly predict the probability circa 2012, and even if I did come up with the fairest possible tax system I have no chance of actually getting it implemented, so it would just cause me frustration.
The people who did really great things in history -- whoever you might choose as your examples -- did they achieve it by being significantly more rational than everyone else? Not really, no. They did it by achieving some baseline level of rationality and then being extremely good at other stuff.
Observational bias. Rationality of thought process in non-technical situations is rarely externalized; unless you talk of scientists, you're highly unlikely to remark on how highly rational he is being. In fact, the only way I can come up with to make such a statement fit in literary fashion is when you're making a quip on someone:
"It was highly rational of Nixon to start the Vietnam War."
Either you're making some deep meta-quip that I don't get, or...