I like this line of reasoning, but I'm not sure it's actually true. "better" rationality should lead your thinking to be more effective - better able to take actions that lead to outcomes you prefer. This could express as less thinking, or it could express as MORE thinking, for cases where return-to-thinking is much higher due to your increase in thinking power.
Whether you're thinking less for "still having good outcomes", or thinking the same amount for "having better outcomes" is a topic for introspection and rationality as well.
That's true, of course. My post is really a counter to a few straw-Vulcan tendencies: intelligence signalling, overthinking everything, and being super argumentative all the time. Just wanted to practice what I'm preaching!