Fulfillment at Any Age

Agreed. Although I have a slightly different perspective that I write about here: Healthy Self-Esteem: An Alternative to Self-Pity vs. Narcissism.

that narcissism is on a spectrum like autism?

I much prefer the term "healthy self-esteem" to "healthy narcissism", because to me the word "narcissism" automatically implies an unhealthy, obsessive degree of self-absorption. So the term "healthy narcissism" is the same as saying "healthy illness", which makes absolutely no sense to me.

Secondly, I am of the opinion that all mental illnesses exist in a spectrum of severity, based on the frequency and intensity of the symptoms/behaviors/traits an individual exhibits. I personally think that the Cluster B personality disorders are all based on (or have the underlying pathology of) unhealthy, extreme self-absorption (aka extreme narcissism.)

In addition I think that the Cluster B disorders are all varying degrees of severity of psychopathy.
It makes sense to me to replace the concept of "Cluster B" disorders with the term "the psychopathic spectrum of disorders."

Those with total self-absorption (the current diagnostic traits of narcissistic pd) who also lack a sense of right and wrong or a sense of remorse, are the psychopaths,

Those who are totally self-absorbed but have a rudimentary sense of right and wrong and are capable of feeling true remorse are the narcissistic pd people.

Those who are totally self-absorbed but have emotional dysregulation and a tendency to experience breaks with reality and paranoid delusional thinking are the borderline pd people.

Those who are totally self-absorbed and act out their dysfunction with hysterics (including acting out sexually) are the histrionic pd people.

That's just my own personal theory; I'm simply the adult child of a bpd mother and enabling, "dishrag" father, not a psychologist or psychiatrist.

-Annie