This is why there are some merit sources that are offering post reviews for different users that for them is deserved to get merited for their high quality posts.
I don't think that these merit sources that are offering post reviews has a minimum rank required, so as long as you're posts are of with high quality (and not bounty reports), even you're a newbie you can still apply to them.

I often see some merit sources circling around different sections like Bitcoin Discussion, and they are distributing merits there. Those newbie ranked members in the past aren't newbies right now because for sure they ranked up already. Those who are ranked newbies as of this moment are either the ones who just registered a few days or a few weeks ago, or they are simply newbies who are posting bounty reports from their bounty campaigns.

More merit = more motivation? Hmmmmm I don't think that's always the case because even low ranked members can still contribute in their own ways. I'm pretty sure that these high ranked members that you are saying see those low ranked members out there, and they know which are contributing or not, and if they see that they're contributing, they will give merits to them.