Here's a thought experiment based on an idea of John Spano, one of our grad students (I modified it in the first version below by adding that the decisions are "somewhat better"). Imagine you could get a microchip implanted in your brain. Whenever you needed to make a decision, it would tell you what decision you should make, and it would be guaranteed to make decisions somewhat better than you would. Likewise, when you needed to figure out something theoretical, it would figure it out for you, and again it would be guaranteed to be somewhat better than you at this. Would you do this?
If the value of rationality is purely instrumental, this is worthwhile. But a life based on the dictates of the microchip just doesn't seem to be a flourishing life. This is clearly true if the decisions the chip comes to are only somewhat better than the ones you would come to yourself. But I suspect that it is also true if the decisions are much better.
At the same time, maybe you should go for the microchip in the case of decisions that significantly affect the flourishing of others. If you are a doctor and a microchip would make better diagnoses and recommendations that you could, then it might be your duty to sacrifice your own intellectual flourishing to the medical good of others.