In my experience, a person is usually boring or interesting based on the company he/she is having at that time. Sometimes, people who are considered boring by others may just be introverts who open up and become interesting only in their own comfort zone. On the other hand, few people who are always seen as the life of a party may actually turn out to be boring when you are having a one-to-one conversation with them.
I think it all depends on whether we share any common interests with a particular person, in which case we may have plenty of things to bond over, which in turn makes the company worth keeping.
Personally, I don't restrict myself from mingling with people based on a boring first-impression, because many of the times, there's much more underneath that boring facade than meets the eyes.
Of course, there are those hopeless loners who really don't or can't mingle, even when the other person makes a sincere effort. Well, maybe such people should be best left alone.