I disagree with your characterisation of Clinton as vacuous, she's an extremely well-educated and competent lawyer and is quite astute and capable, politically. Ultimately and unfortunately, however, I suppose Clinton was arguably more Washington DC establishment, she was more 'inside the beltway' whereas Harris' background is California senate then veep, she seems more fresh and new and approachable and 'of the people' iyswim, with her folksy ways, her Converse and jeans, etc., much more approachable and warmer and more empathetic than the arguably political wonk/dorky Clinton who seemingly went through the motions making/baking cookies. Where that kind of thing seemed forced and fake with Clinton, you can imagine Harris getting stuck in and enjoying that.
Whereas Clinton's credentials were more easily questionable, like: 'So her husband was president, but how and why does that mean she's got the credentials/experience to stand for president?' No disrespect to Clinton intended, she apparently did some good work re health policy etc while her husband was in office, but she was/had always been more in her husband's shadow, whereas Harris is the one who's been the public figure in her marriage, so it's easier to visualise Harris in a leadership role rather than playing second fiddle to her husband.
Women shouldn't be judged on who and what their husband is (or their wife/partner), but the reality is that that happens, just like male politicians on the 'first lady' potential of their wives (or spouses).
Btw, I agree with you re her making a point about the government keeping out of private affairs, that will definitely play well with Republicans.