Hm. It probably needs a little something else to warrant being its own card. +2 Cards would work, but may be too similar to Vault. Maybe +1 Card/+1 Action?
I mean, this usually want to be the last action you play, topdecking terminal collisions. So +1 Action doesn't really work here, except in draw-to-X, which isn't common enough to warrant this. It wants ideally strong terminal draw. At +2 cards it's probably a bit weaker than Vault, because if you're playing inverse storyteller/BM, you have to topdeck your green cards to gain Provinces. Then again, Vault is strong enough a $5 to warrant giving the other players a bonus, and in some cases you'd prefer inverse storyteller, so maybe $5 would be okay? Still seems weakish for $5 and too strong for $4. Drawing 3 cards makes it strictly better than Courtyard, which already is a premium BM enabler.