/me leans in
I’m not one for ‘magic internet points’ but I will say — as a part-time boardgame designer — that set collection is a pretty strong mechanic that people are more than happy to work towards. A lot of badge schemes lean on set collection to increase participation from those who are already participating.
My case in point here is 24pullrequests.com which saw ~16k people contribute a pull request a day, every day during December. The only additional reward being a calendar of gifts and a public profile.
Also I am commenting because I have a massive thread of emails on this subject in my client. Activity attracts activity