Sometimes. You've got "The Enemy Within"
, with Kirk being split into two halves, one "good" and one "evil", and the evil one is more emotional, more brutal and passionate. There's "Mirror, Mirror"
, with the universe of barbaric Star Trek
characters, which ends with main-universe Kirk appealing to logic to convince mirror-universe Spock to change the course of the Empire (that universe's Federation).
Generally, though, it's the plot itself that endorses rationality. The Enterprise
encounters some planet where people are making themselves miserable with some irrational belief system, and Kirk uses the power of rationality to set them straight.
Anyway, as I said in someone else's LJ just last night, Vulcans aren't really logical as much as they're stoic. Or perhaps Stoic
. In "The Ultimate Computer"
Spock is amazed when a computer feigns being destroyed in order to lure an enemy into a trap. There's no logical reason for the confusion -- feints and gambits are perfectly logical behavior, requiring only a theory of mind so that one can attempt to make predictions based on an opponent's likely reactions to one's own behavior. But feints are dishonest
, and therefore a violation of the Stoic ideal of virtuous behavior even in the face of doom.