I am not sure, but how many clues you can get from "Visions" (CotDP) with a Spell that cost "special" ? 1 clue ?

I always assumed that "special" meant 0 in this case. The sanity cost of the spell is 0 until you increase it by spending sanity when you cast it, but when you "crunch" it for clues, you're not casting it, so you can't push the sanity cost above 0.

So, 1 clue total.