Even though you explicitly state that you win based on who makes the most noteworthy posts, I am pretty sure that a lot of spam will be generated by this campaign. Might be smarter to accept people based on their previous posts (but that is my personal opinion). I do recommend you to use escrow. A lot of people got screwed in the past, which makes them wary of joining new signature campaigns. If you have any questions about that, just send me a PM 
After further thought...and a few people have said it, I believe this sort of campaign may cause spam (which is complete opposite of what I want) So I may scrap this campaign, go back to the drawing board and think another campaign idea up that may lead to more meaningful posts.
Thank you for your advice.
and of course my budget for the new campaign will be around the same and as always I understand as a new member I will escrow.