Its been a long long long time since ive seen spit used by anyone not level 1, who just pick it because its an attack they have available.
Spit already has a pretty good mana damage ratio, but since it isn't as cheap as missle people are no longer interested. Spit used to be okay in the slower days of wands where people sit on one tile and curve it around columns but those days are over.
I think a small buff to spit, increasing damage to 20, will help bring spit alive again. Currently electric fist is one of the only reliable, cheap, quick ways to take out demon. But i dont want to see everyone running fist in every build just because demon is popular. With the buff to spit, 3 spits will take out demon quickly for a small mana advantage.