I think people doesn't care about it whever campaign's rate gone low or not. Enrolling sig campaign earning bitcoin and it should just consider as bonus for posting. For me as long as I can earn by posting , no matter how rate they are , I keep enroll to any campaign even there are only 1 sig campaign left on this forum with lowest pay
I agree that it is consider as bonus for posting. However, I will not join a campaign if the rate is too low. I would rather use my spare signature space to advertise my Bitcoin related website. If I do not have a Bitcoin related website, I would link it to a useful thread on this forums such as
https://bitcointalk.org/index.php?topic=990345. If not I would use it like how others in the past is used - asking for Bitcoin tips in the signature.
What rate do you consider to be your minimum for participating? What rate will be too low, that you'd walk away from?