It doesn't explicitly promote rationality, but in terms of demonstrating rationalist virtues in action I believe that the Stargate franchise, or at least the parts I'm thinking of* do a pretty good job.

I've counted nearly a dozen features of physics and technology that can be used to create clones in the Stargate universe. The most straightforward (and least 'fantasy physics' based) example is the robot clones of SG1 that were running around the universe for several years. Yet while the Stargate team have access to that kind of technology I don't see 10,000 each of McKay and Carter working in a research lab. Nor do I see 1,000,000 clones of Daniel Jackson sitting in rooms meditating to ascension.

If the fate of the universe is at stake and you have the chance to become a demigod then you take it. If that isn't enough then you make yourself into an entire pantheon. You utterly obliterate, neutralize or render laughably insignificant any threats.

Although I think you are on to something. There is one character in particular in Stargate that seems to behave rationally: Ba'al. And not just because he created an army of Ba'als and tried to take over the galaxy. There are all sorts of lessons that can be learned from him. Not least of which is the ability to cooperate effectively with people with vastly different objectives when it makes sense to do so.