Here's another data point for the discussion.
I've started paying for a flickr pro account 2 years ago. I pay full price for it, and I'm happy about the price I pay for what I get. I only have ~600 photos in total and have had my free account since 2007. I just like to upload little and only what I personally really like. In theory, I could downgrade back to my old free account but I simply do not want to.
The thing is I have gone for the flickr pro account not for a 'popularity fix' but to support a platform that simply has no equal. To me, flickr is still the place to go to enjoy the work of several really talented photographers. It's profoundly different from Instagram and other similar cr*p because on flickr I do not feel like I'm being fed content reordered and reshuffled to maximise my consumption of advertisement. I pay, I can tag and order my photos in many ways, I can keep a historical record on the evolution of my photography over the years, and importantly I see things the way people post them according to their artistic vision, ordered in a temporal fashion. I do no see, nor want to see, any ads sprinkled in, or content re-prioritised based on an algorithm.
As for the 'they want to pay for pro to get their popularity fix/they're insecure", Personally, I only post film photography content and the film photography groups I follow are extremely active and increasingly filled with amazing content, as people in my age group start to leave instagram and facebook and join flickr, while the old scroungers with 12k photos on a free account are gone and their mass group posting habit is vastly reduced. As for myself and groups, I do post to groups, but although I could post to 150 groups etc for my 'popularity fix' I only ever post to at most 20ish groups, which I know are extremely active and thematically coherent. Some of these groups are so well moderated, and filled with such great content (despite my mediocre contributions) that it feels like being at an exhibition. No fighting, no inane comments by gearheads, no ads, just silent enjoyment of photography.
What's also interesting is that with other people I am busy taking over old abandoned groups filled with great content that dates back years. It's a pleasure to clean up these groups and bring them back to their former glory, at the same time getting new blood in. Moderating also means taking some difficult decisions of course. The first ones to go are of course the scroungers who, on groups limited to 1 post per day/week, try to post more than one item from each of the several free accounts they have. Easy to identify, easy to ban.