In my opinion, yes it is worth it to continue to send supportive emails to (PSA's) and (CSA's) who have only 0-VersaPoints, because if it were myself who was unsure or maybe even skeptical about staying active in a program; it would encourage me to know that someone still cares about my future and refuses to give up on me.
WHO KNOWS- In the near future they could become your most active members...
So Yes, I Would Definitely Continue To Support Inactive Members.