I wonder if theres a correlation between the freshness of a follower and their value. I wonder if you're more likely to engage with something shortly after you follow.

I've definitely done it myself. I follow because I'm really interested, so I interact with the posts on the new thing, and gradually I get less interested as the content becomes less novel. Just as an example, I got really interested in the CNCF and followed them, but after a time, my interest in updated from them waned. I went from wanting to see everything they were doing, to only caring about major updates to software, to really only caring when something new joins the CNCF.