Recently I ran into this problem and was close to deleting the hubs that weren't getting any traffic. Than what I did instead of deleting them was look into keywords through good adwords, seen what was good and what was not working for those hubs anymore.
I also used the hubpages title tuner to get the titles a little better and added in some keywords into the titles, this helped out a lot because out of the hubs that weren't getting any traffic, they are all getting around 10-20 hits a days and I see that increasing a little more as time goes on. Another good thing I have done with some of those same hubs was re-write some of the information in there and make them more outstanding.
Sometimes it only takes a little time and patience to figure out what is going to help increase your traffic to your hubs. Not everything that someone else does is going to benefit you.
A few other things to try is type something into google, bing, yahoo that reflects what your non-traffic hubs are about and see where they stand page wise, if they are in the top three pages than it could be your keywords just aren't working for that hub and you might have to re-do them but that is easy once you have an idea of what is missing.
Writing more hubs wont compensate for the ones not getting traffic of at least it didn't work for me, the new hubs got their own traffic as you want them all to get some type of traffic to pull in some type of revenue, Try the topic tuner and the keywords and see if that helps your dropping hubs.