Thanks! My hunch is that song-writing does aid recall, though I'd love to conduct a study to see how far that really goes in terms of depth of understanding and duration of memory aid (years? decades?). I know that the popularity of the videos among student's peers definitely aids in teaching. For example, every kid for several grades knew all of the words to "That's Metal" (https://www.youtube.com/watch?v=BlBKsbCLY24) when it came out. And I guarantee that every one of them could tell you that metals are shiny, malleable, and have something to do with loosely held electrons. The more interesting question to me is whether the writing process aids with depth of conceptual understanding. I find that this is the case if the videos are used in the context of a class where students are delving deep into the material.
Re: lyric writing. Giving it enough time for multiple drafts has been the key for me. I have some specific spreadsheets and tools that provide some guidelines that have been helpful in terms of aligning content with flow and rhyme scheme.
Re: culture, I try to get the kids to talk explicitly about cultural appropriation (this video by Amamndla Stenberg can be a nice starter: https://www.youtube.com/watch?v=O1KJRRSB_XA), and to include some education about the history and influence of hip hop (so that their conceptions are not left to what is on the radio and on television). Then I get them to find examples of "educational music videos" that they think are examples of "getting it right" and those that are embarrassing/offensive.
One struggle is that writing lyrics doesn't come naturally to everybody, and takes some practice. Group size is also really important, and you want to make sure everybody is able to contribute (but writing a song by committee can be challenging). For all of these reasons, the lyric-writing stage is the hardest and most important. It takes a lot of iterations to get something that is accurate, clear, catchy, and tells a cohesive scientific story.
Once you get those lyrics nailed down, the audio and video production are so exciting for the kids that they are willing to devote a significant amount of energy outside of class time to shooting and editing.
The "headshakes" or pitfalls that are important to avoid surround cultural respect. If kids or teachers don't have a deep understanding or respect for hip hop and hip hop culture, they run the risk of embracing stereotypes that will be embarrassing and offensive.