Sure, RivAngE has some kind of point that there can be something a bit whimsical about merits, but at the same time, it does not seem healthy to either get psychologically obsessed with getting merits for decently good posts and it comes off as a bit petty to post something like "I wished I could receive more merits for my 'valuable' posts."  It seems to take some credibility away from your posts (and even insulting other members from making their own assessment about the "value" of your post) when you self-assess them as "valuable."

Just showing up and posting on a regular basis does seem to cause merits, and reminds other members of your existence.  Sometimes, I come across a member that I want to merit, but I don't want to merit based on merely one good post that I see, so I put the member on a "watch list" that I maintain, so if I don't see any further posts from the member after a certain time I might remove the member from my watch list - or I might actively go through the members prior posts to find a post that I believe is worthy of a merit.... So, there certainly can be some whimsical practice of the merit system that can be partly attributable to considerable individual differences regarding what they deem merit worthy and/or just if you catch them on the right day (merit sources included).