I do not think it is a good idea to remove a hub when traffic reduce or after some time.
I suggest you to improve your hub by adding some fresh info, change the tags and backlinking if your traffic go down. Also link your hubs between each other that would help to increase the traffic and page ranking as well.
Anyway if you delete a hub has high hubscore would effect to overall score. (average will go down if you delete a hub which has high hubscore than the average).