My best insights have often come early in the morning when I've still been shaking the sleep out of my head, in the free-association state that accompanies awakening. The cognitive superstructure that assembles and deploys cached thoughts, I find, takes somewhat longer to wake up than the rest of my brain, making for periods of enhanced spontaneous creativity. In this state I often feel strong impulses to create artistically as well.
If I could find some drug or meditation technique that could reliably induce this state, I believe I would be a happier and more productive man.
Here's something big that I don't think anyone's mentioned yet. Rationality isn't the only meta-skill; you are born with the incredible ability to learn new skills, and as with most other traits, skill-learning aptitude varies between people. But more importantly, a lot of people don't realise that the skill-learning mechanism can be honed; the brain circuitry responsible for picking up new tricks grows and develops in response to use.
There are reams of anecdotal documentation, and probably some properly conducted tests as well, that bear out the local form of this phenomenon (after you've learned three second languages the fourth is easier; if you can play badminton and volleyball, then all other things being equal, you'll probably pick up tennis better than another absolute beginner). I suspect, without much justification, that this also happens globally: having exercised your skill acquisition centres in learning to play volleyball, learning to speak Russian is going to be a tiny bit easier than it otherwise would have been.
So, apart from being extremely good at pure maths (to the extent that it ought to provide me with a prestigious career), that's my most useful skill: l'm pretty quick at picking up new ones.