I would look at it this way; even if there's nothing wrong, it's always good to take a new pet to the vet soon after getting them. Better to establish a relationship with a vet before there is anything wrong than to meet a vet for the first time when your baby is sick and you're in a panic.
Now, that being said, a runny nose can be indicative of an upper respiratory infection. No big deal so long as you catch early and get it treated. Usually just a round of antibiotics. However, if it's not dealt with quickly it can become pneumonia, and no one wants that.