With the help of campaign managers, bitcointalk will be more active if they bring back the old way of accepting participants, like accepting even jr. member ranks. Most campaigns now only accept Hero to Legendary Members. I think Jr. Members rank is okay with the payment even if it is only $10 per week or less. This would also help the campaign and save some funds. But assume high amount of spam post once this once is implemented.
There must be a reason for campaigns not bothering with junior members. Sure, they could pay them much less and probably there would still be takers, but if the cost of managing junior members (i.e. checking their posts, making sure they're not breaking the rules, making payments etc) exceeds any potential benefits, then it's simply not worth it.
Junior's signatures are simply hardly visible on the forum, so they're not very good in terms of either creating more brand awareness or getting people to click on the links.
Just be patient, stay active and try to rank up.