Suggestion to disqualify junior members from taking part in signature will definitely benefit not only Junior Members but also the forum itself.  Because to rank up for the purpose of taking part in signature campaigns every Junior Member will have to earn 10 merits and for this he will have to read more and more.  It will increase his knowledge and he will be able to post good posts. Initially it may not be welcomed by Jr Members but bitter tablets are always given for betterment of the people.  So it will do good in future. 

But IMO not rewarding with merit to good post  just because the person could not post quality post in the past or taking part in some bounty;  is not good decision,.  Every good work done at any stage should be rewarded if it is really reward-able.  And if every merit source is of such view and not sending merit to the quality post ; then how can we expect a newbie to rank up.