I feel the biggest challenge is to actually get people to post in the first place
True, but I think people have been actively discouraged to post too many messages to ros-users in the past. I’m in the same boat as @Daniel_Stonier: I found out about amazing packages (or amazing new functionalities, like topic statistics) only a year or more after they were initially released. Since there weren’t even announcements to ros-users for those great things, it made me reluctant to announce stupid little driver packages to ros-users, because they are not relevant for 99% of all people (unless you happen to own such a device, in which the information that a driver for it is now available becomes very relevant).
Perhaps the switch to Discourse will encourage people again to post more announcements, even for small packages.