i believe this concern was addressed in the informational hub written by a moderator a few weeks back when the changes were introduced. The Zzzz's do not affect your ratings.....I'm not sure about earning potential. Check the learning center. Answers to a million questions are there.
To remove or not to remove, is your own individual decision. If you like the hubs and put a lot of work into them, you should keep them, IMO. If you don't think they're worth keeping, let them go. In 14 months, I have only deleted one hub and the reason was, it was terrible from day one....and as many times that I edited it, I still thought it sucked....so I gave it the boot.