Absolutely! Characters loving themselves or coming to do so are two of themes I strive to include wherever I can. While that sort of confidence is not always going to be a feature, it is a big part of why I insist on the “sex-positive” goal for my stories. I do think sometimes that confidence gets wielded like a club, creating couples with power dynamics which are unbalanced to an unhealthy degree.
Especially once that confidence becomes arrogance or self-absorption. It is a character crossing that line which makes me start having issues. If one is unable to see their own flaws or their strengths in others, that is the moment, for me, they start down the path of “evil”. Which probably seems extreme but my definition of evil is “ambition, action, or cause with a deliberate lack of concern for others” and many of those stem from people not being able to see past themselves.
There is something to be said about confidence as inoculation for “reprogramming” as someone with a strong sense of self-worth can resist the influence of others–which is, I think, an underserved dynamic in transformation. So much of the genre is about hedonism, about giving in to the new sensations, that sometimes existing personality is overwritten in that pursuit. It was a lot of the reason I wrote Jess O’Doyle the way I did. Sure, her body has become a hyper-sexual male-gaze fantasy, however, she is still herself. Her confidence about who she was–bolstered by the mishap with the formula–ensured that she endured the attempted murder of her personhood–and there is the point in the other direction. Just because she has the appetite of nine women now, she tries to view her partners as people still and not just dicks, tongues, or fingers to satisfy her needs.
So, yeah, the point I want to make, explicitly, about writing characters who love themselves is try to make sure they can still see themselves in others and thus not end up assholes–or, failing that, have them be Captain Britain and take generally harmless but still cathartic pratfalls because of their arrogance.