You know I've been thinking about something like that myself. My overall score is decent, I suppose, but most of my hubs seem to fall in the mid seventies range. Yes, there's one or two in the eighties, and one spends a fair amount of time in the low nineties.
One starts to doubt himself, doesn't he? I suspect you and I, amsmoving, will just have to give it more time. WIth increased outside traffic, bigger numbers that way, I think the scores will go up. I don't think you should interpret those seventy scores to be a reflection of the quality of your hubs.
The ways of HubPages scoring is a mystery, as you know.