The hubscore is how a hub meets the criteria of Hubpages. It is an internal thing and nothing to do with how a hub is performing in the real world. But, the hubs that have very high hubscores are sitting ducks to plagiarizers. So, are our hubs that are marked as "hot" or "best." Thank goodness the new profile do not highlight our best hubs anymore.
I have only one hub out of over a hundred hubs that keeps getting 100 hubscore. It was performing well before, but not "the" highest performing hub. A few months ago, it disappeared from engine search. Why? Because it was copied numerous times and I didn't know about it. I just recently filed so many DMCA complaints, but my traffic have not returned to normal to date.
Oh, to answer your questions:
1) How important is the hubscore on our hubs? - Not important at all.
2) How are they calculated? - Only HP knows.
I wish you the best here on Hubpages, sweetzara. What a sweet name! Cheers! :)