Well, life is a journey. And obviously you shouldn't limit your attractions by typology! Having said, that, I perceive infj/enfj as almost incest.
I DO prefer similar types as close friends, but as I'm working on developing my Ti (my supposed tert function), I could see that broadening a bit now.
I think that similar types are safe, or safer for one's pyche. I think they can be a good sounding board if you are in a place where you don't want too much conflict in communication or don't have much energy to expend in a relationship. I also think, and this is definitely not everyone's experience, obviously, that to be fully challenged and thrive as a well-rounded individual, or to explore all the little places that exist in yourself that you (one) are perhaps not even aware of, you would do better with a type who perceives and judges data in an opposite manner. But that's me. I like to be challenged in various ways. It comes down to that I think. What do you need right now? If we live until we are 80, and we start having relationship at 20, we have many years to relate intimately with others, and why limit it to one or two or three individuals? If you want that to be one person however, one s.o., you might find someone of opposite disposition is preferred to get you through the long haul. Shorter-term relationships, as they relate to type, are of not as much consequence.