After the implementation of merit system the activity of mass user has been decreased vitally. Yes the spam posting has been decreased also. Peoples are targeting for merit, so they are investing time for quality posting. Therefore the activities are decreased than previous.But the merit is important to level up.
I don't think the spam posting decreased and quality posts increased.I can only see that people are making more lengthy posts than before but still with the same spam level.Yes they are giving more time to create the lengthy spam posts. 
We can't completely take out the spam from our forum until no more signature campaigns in this forum because more people are posting here for the sake of completing their quota for signature campaigns.
But I saw that new campaigns are launched with merit based acceptance so now people may concentrate on getting merits hereafter because most of the people keeping signature campaign rewards as their main income.
The level up is not that much important than participating in the signature campaign.