How important is nepotism in the grand scheme of things?

Nepotism exists, but it exists because of a 'consensual inertia' in public dialogue, maintained by an inability to "talk" openly, because the felt associations between certain words (such as 'shame'), situations, and concepts, prevent the person from accurately perceiving its own defensive effort to deny an unwanted reality.

The mind is not knowable without conscious effort. In itself, it is reactive, reflexive, and so continuously stereotyped. To "know thyself", means to dig down beneath the moment to moment changes in your phenomenology, and ask yourself, "should I be doing this?" "Is this productive? "In this reflex, this moment of thought, am I needlessly worrying myself"?

So nepotism is the result of evolutionary processes which favor "kin selection" stereotyped across conscious states such that it is "easier" - or more familiar - to form evaluations that bring the "self-objects" into day to day activities.

It is not essential to our being but subject to the processes that organize our reflexivity i.e. its open to deconstruction by reflective consciousness.

Human consciousness is exceedingly complex. I can hardly even 'explain' to you how we can 'reprogram' ourselves without going into the nuts and bolts of how communicative processes act upon preset genetic sensitivities that feed individual minds into the existing 'cultural scaffold', such that every mind comes to define its own value (or worth) in terms of culturally set standards. Culture, of course, refers to the "collective intentionality' of the world we interface with. It's first appearance is in the form of our primary caregiver. And it becomes more and more complex as different kinds of relationships (relational information) act upon our organization as persons.

Ultimately, love is more intrinsic to the nature of human consciousness than "nepotism". As others have written, the task of man is to 'widen the circle', so that cultural and social processes which "gate" human consciousness do not interfere with the natural sympathy that would otherwise exist between two self-conscious beings like ourselves.