Well that's the end of my journey with spirals. I figured out how to make the shapes that interested me in a satisfying manner. The only thing still lacking is to figure out how to make the spirals wider without having to attach more balls of yarn.
I just had a thought about that! Why not just make taller stitches? Like instead of dc (2c), use 5c, or for even bigger ones 10c (these numbers are totally arbitrary). The obvious problem is that there will be gaping holes. That can be solved by using linked stitches. The corners would be interesting to figure out, but probably doable.
Anyway, now that that rabbit trail is over, let's summarize what I've explained about spirals.
I've found or written up patterns for the following shapes:
Circles (really 12 sided polygons)
This is hardly an exhaustive list of shapes. As I write this, I realized that triangular spirals are also possible. Any shape, at least regular polygons, can be made with spirals. Hopefully you can figure out how to make a heptagon spiral if you really want to by looking at the principles for the more normal shapes.