I have heard it can help your hubscore to delete poorly performing hubs.... but my question is, why would you want to do that?? Hubscore is just a number. As long as you are over 75 (which you are), your links are dofollow. So your hubscore is just fine. Why would you want to delete your old hubs? I would not recommend deleting hubs purely to increase hubscore. Your old hubs may become popular again and earn you money sometime, so I would not recommend deleting them purely for hubscore purposes. (I have only deleted one of my hubs, and that was a never-published one & only because I changed my mind about wanting to place it on Hubpages). That is just my point of view on your question though. Maybe others might come up with a reason why your approach could be a good one.