For what it's worth, I think we talk of Heavenly Father so much more than Heavenly Mother because our scriptures were written by men. Period. Full stop. If we had more scriptures written by women in matriarchal societies . . .
I really like the concept of Heavenly Mother, at the very least just to state explicitly that women can become like God just as well as men. There's so much cultural and historical crap wrapped up in seeing God as exclusively male that I'm glad Mormonism makes the claim that such a construct is wrong - even if we have next no nothing in our actual scriptural canon to talk about her in anything more than broad, generic terms.