I believe that it is UNNECESSARY to send out everything that you do; except when it benefits your receivers. I would suggest staying in regular contact with ALL of your ACTIVE affiliates. There is no set number, but remember to keep them updated with all of your actions.
For your non-active affiliates, it is wise to, at least, send them a notice twice a month. You should send them updates that might pertain to them, should they decided to become active in the future.