You score on profile should be at least 85 (I am working on that right now) to have links pointing out of HubPages 'do-follow'. If you are, for instance, trying to send some authority to your blog and your blog returns authority to your hubs, PageRank flows in both ways.
If your score on profile drops bellow 85, your blog will not get any benefit in terms of PageRak, it will loose authority and this means all links coming from your blog to your hubs will be weaker although not necessary useless.
For people who depend only on keywords with low competition where internal linkage could be enough to rank, your scores are irrelevant (well, if they still manage to get traffic, scores will go up anyway). But with more competitive keywords you will need some kind of support through backlinks and in this case 'do-follow' links could be very helpful.
This is in my opinion the most important impact of hubscore on traffic, although not the only one. Score on profile is related with score of your articles and articles with lower scores have lower positions in internal rankings what means less exposure to visitors and SE bots. Often switch from do-follow to no-follow and back can be interpreted as sign of low trust for particular site (in our case subdomain of HubPages), what can have huge effect on rankings in SE. There is also a psychological effect on other users of HubPages who sometimes don't take seriously other users with lower scores etc.
My two cents:)