Have you seen pictures of great musicians, physicists, mathematicians, philosophers with awesome faces dived deep into the realm of contemplation? How do you feel about them. For example, how do you feel about Albert Einstein? I feel greatness, smartness, and many more attributes.
Smartness is a positive attribute. We may even say that it's an absolute good attribute, that is, no matter who you are, and what you do, people always feel that smarter you is better.
At the other hand, we have the concept of psychological association.When people see a good guy, they also trust his/her work. Here, goodness (or maybe smartness) is associated to the better work.
Thus, I believe that smartness is important for a developer. But hey! wait a minute. How can you behave smart, when you're not?
I think the main question is here. Many types of intelligence exist and apparently some people are much more better in many of them than others. In other words, when you're not intelligent, then you're not intelligent (sorry about tautology, just for emphasis). Thus, don't try to show something that you're not. If you're intelligent, then you'll behave intelligently. But if you're not, stop trying to mimic one.
However, I think more important than being intelligent, is to be diligent in programming.