I was assuming you meant epistemic rationality. I certainly believe creativity is great and an instrumentally rational goal.
My guess is that creativity has something to do with a feeling that some passing thought is interesting enough to be worth pursuing, but that doesn't mean I know whether everyone has enough passing thoughts to pursue.
I dunno if there is anyway to improve the generation of thoughts, save good genes and around 10000 hours of practice.
Having said that, slatestarcodex did have some interesting thoughts on how creativity might be simply the mind moving out of the ruts it creates for itself, the opposite of focus, explaining why creativity is sometimes associated with mental states such as being half asleep, on drugs or bipolar/schizophrenic etc.
As far as passion and interest goes, I suppose that this should come naturally with general good mental health.
A lot of Less Wrong frames becoming more rational in terms of correcting biases. When Scott Alexander is asked how he does it, he doesn't seem to actually have an answer-- if I recall correctly, he's just said that all he's got in his life is his job, his girlfriend, and his blog, which doesn't begin to explain his remarkable flow of interesting posts.
It's a good thing to have fewer and weaker biases, but it's better if de-biasing can be applied to new ideas which have a good chance of paying off.
Is there LW material about creativity that I'm not remembering? Any recommendations for information about creativity elsewhere? I'm especially interested in material which you've seen help you or other people become more creative, as distinct from material which has been plausible and/or fun to read.
Edited to add: While I think this is a generally applicable topic, I also have a local interest. I'm fond of LW, but it seems to be in a doldrums, and at least part of the cause is a lack of interesting new material.