That's a difficult question since you need to define "post quality."
IMO, the quality of writing is subjective, it depends on who reads it and who grades it. It's even more challenging in the public forum where not all members have the same education level and major. But if the question is phrased differently such as "Do members with higher rank make more quality posts according to my taste?" The answer is probably a "no" for you since you make this thread. It's also a "no" for me since I have a different taste for "quality posts."

It can be "no value" according to your taste, but valuable according to others. But it also can be because the members in question only post for a signature campaign, or got the rank before the merit system was implemented. It's difficult to talk in-depth because there's no real example.

Anyway, I'd say don't lose sleep over this as you control what you want to read and respond to. If you find it annoying, simply add them to your ignore list or just ignore them and don't reply.