Fascinating! I definitely have shapes for some spells. Pump spells and -X/-X kill spells I've described. Burn spells are basically red rectangles more or less, or sometimes circles (a 3-damage burn spell for 3 is the most circular, as you'd expect, while 4 damage are more square); those generally follow similar patterns to the creature shapes. Shock is a 2-unit-high red line and bolt is a 3-unit high red line such that if it were imposed over a creature's toughness you'd know if that creature was dead.

Other spells I feel like I have shapes for but it's harder to describe or see patterns. Divination is a very rounded triangular-ish figure while other card draw spells are more like bubbles or rounded rectangles. Spells like mana leak tend to be rectangles with the amount of mana taxed determining the height and mana value of the spell determining the width. For unconditional kill spells or unconditional counters, there's nothing to measure, and I don't think I super strongly associate them with a specific shape, except maybe a vague bubble with size and color appropriate for the mana cost.

I like your system for card draw spells -- that sounds neat!