Maybe this is pure anecdote, but I've noticed that more intelligent (especially hyperintelligent) people tend to have more attention to give in a conversation. They're more present. They can follow what you're saying, or lead you in directions you hadn't considered (i.e., by surfacing insight). This makes for a dynamic, interesting conversation that -- to your point -- forces you to stay alert and engaged with them. The exchange is more engaging on both sides, regardless of subject matter. And subconsciously, we tend to think more highly of people who seem more engaged with what we're saying.
Humans being human, that's not universal. While I've noticed that some very intelligent people are more pleasant and enlightening to talk to, some others just can't seem to be bothered to give you their full attention. It's as if you don't meet their "worth paying attention to" threshold. Symptoms can be anything from a vague dullness of the eyes, to glancing or even reading their monitor, to just total loss of engagement in the middle of a sentence.
But again, humans being humans, that's not limited to very intelligent people.
Dale Carnegie says that the secret to being a good conversationalist is to be a good listener. People like to talk, especially about themselves (and neither Dale nor I mean that in a bad way). As an introvert, this realization and learning how to ask good questions (such as ones that don't have binary yes/no answers) made learning to converse with new people easier.
