Great point about muscle memory, I found it fascinating to learn Spencerian as it kind of distills the essence of writing to a surprisingly low number of forms (7 or 8 I think?), a kind of local optimum for Latin-based cursive. The hardest thing for me to learn about it, with which I still struggle, is keeping the arm posture correct and using the upper, rather than lower, part of the arm for control.

I also found it really interesting to discover that the prescribed 52 degree writing angle for Spencerian is almost exactly what you get matching the diagonal on an 8.5" by 11" piece of paper (I'm surprised that's not more widely known!). Thus, rather than a difficult and seemingly arbitrary requirement, it's a super easy way of attaining consistency by simply rotating the page so its diagonal goes straight away from the writer. (If you're using US Letter paper, anyway)