Yes Merit works really well. This forum has a lot to knowing thing. Many newcomers here come only for work. Many people do counter-work without knowing it.
Newcomers come here to "WORK"

Is bitcointalk an office for you all? Or is it where shitposters vomit and crap everyday in order to get paid by increasing the ocean of shitposts? And what exactly is counter-work?
Forum are losing popularity with unwanted writings. Merit can only provide one person for good work. So I think Merit is one of the ways to know and understand everyone's personality.
Good Work is not equal to merit. Period.
For now there are lot of accounts tagged because of merit system they taking advantage to ranked up easily that is why i think yes, merit system helps the forum a lot to avoid spammer and account farmers.
This is an indirect effect of the merit system. Its main function is to weed out those people's post which dont contribute to the discussion at all and to give some incentive (by ranking up) to those who make quality contributions to the forum.