First time I played, I couldn't figure out how to close the spell book — I realized this time that there's a white arrow on the light yellow page.
Maybe putting the spell UI on the bottom of the screen, toolbar style, instead of covering the middle, would make it easier (and juicier) to see what the spell you just chose did.
I didn't play long enough to have valuable opinions on the game loop — except that I felt like I soft-locked myself by buying the Spinner too early and not knowing how to turn it off, so I couldn't do the spell that takes threads anymore (Spinner kept eating my threads.) EDIT: Oh, I see you're planning to change that.
The spirit's animation feels a little mechanical but I do like the leaning and the overshoot!
I like this concept and want to see how you develop it further! Cheers!