I think the case for misogyny is a very strong one, and I would bet that a psych evaluation will bear this out. Yes, as he was approaching 40 years of age and recognizing that he was no less utterly dependent upon strong women for support than he was when he was 4 years of age, JS likely grew increasingly resentful of his own incompetence and dependency and was likely feeling psychologically castrated in recent years. I don't think it a mere coincidence that the woman he murdered in the present case just happened to be an extreme example of a strong, uber-competent female, and a doctor at that, though in obvious contrast to her petite, and seemingly vulnerable, physical stature which likely encouraged him to be aggressive with her as much as her social status and spiritual strength infuriated him.
That being said, two things stand out about this case which mark JS as a serial killer: 1) He bound his victim in a manner consistent with sexual sadism. 2) He set her corpse on fire for reasons which are not entirely obvious.
Had JS simply "snapped" during an argument and strangled his victim in a blind rage, there would have been no reason to have hog-tied her. He tied her up in such a way because he found it sexually arousing to control and humiliate his victim in such a way.
What would have motivated JS to set his victim's corpse on fire? Sure, serial killers have a peculiar penchant for pyromania, particularly in their youth, but there was likely a very practical reason for what he did. Most likely, JS, like BTK killer Dennis Rader, masturbated upon his victim before or after he killed her. Thus, he set her corpse on fire in order to destroy the most damaging DNA evidence, namely, his semen.
JS fits the profile of a serial killer on multiple dimensions. Therefore, considering his age, it is likely that this was not his first murder.