Honestly, I've given up trying to understand hubscore :)
I was off of hubpages for a period of a few weeks where I didn't write or comment, but would check my page once in a while. My score fluctuated from 86 to 92. Then I come back and begin reading and commenting and posting and my score drops from 90 to 88. Go figure. Hubscore is something you really just need to not pay much attention to. Write quality hubs, find new hubbers, comment, post in forums, answer questions. Anything to both engage other writers and drive new readers to your hubs. Also, a big thing that will lower your score is to just follow a lot of people without reading or commenting their work.