I jumped in late to the jam but still wanted to code a fresh submission. I was intimidated by the number of rules on the jam page. I think many people (although not me in this case) just want to join game jams simply to submit things they've been working on, for exposure and feedback, which they don't otherwise have a venue for. This was my experience running another literal no-effort jam over the holidays. You might get more submissions and random enthusiasm if you made the rules more minimalist. However, then submissions might feel less relevant and thus undesirable -- not sure how you'd feel about that possibility.
This being said, I think the rules all make sense, and synergize well with the provided code/assets/theming. I plan to continue to use the democart as a reference point. My suggestion would be that, while listing the rules against a bright red [delightfully festive!] backdrop, add lots more pictures. Pixel art is one of the best languages around, I find. Add a blown up image of the spritesheet on the jam page, "ONLY use THESE SPRITES," could do the same for the soundwaves ("ONLY use THESE COOL TRACKS by THIS COOL PERSON!") -- then potential jammers see they have an opportunity to use really awesome assets from a supporting community, instead of feeling like are prohibited into following rules.
Positive psychology! Holiday cheer! Fine print can always go lower down on the page :)
Another thought -- I don't do many jams, but maybe themes weren't necessary? I think a more elegant solution would be to let the sprites and assets guide the theming. It felt like they really wanted to! Sometime prompts are inspiring, but this jam had so much goodness that I just found myself trying to make my code fit one of the themes at the last minute.
But now I'm not entirely sure of these suggestions. The jam seemed to want to appeal to both new programmers (being in P8 and having lots of easy-to-start assets) as well as more experienced ones (given the complexity of some of the code and associated community). In this sense, I think it succeeds very well. The assets, mystery content, and retro appeal definitely bridge those two groups. Maybe put even more links to PICO-8 communities (Discord, BBS) on the jam page? With big PICO-8 style pixel art buttons that beg to be clicked?
All that said, this jam was really fun to follow and incredibly well thought-out in its metagame and theming. Would be great to see it get bigger and/or better next year