If Alms was just un-buyable with any Treasures in play (like Grand Market with Coppers), that would be great.
Especially when you played a Crown in the Action phase, forgetting it would disqualify you from buying Alms, but then you chose not to play the Copper in hand to get up to $3 since you could get a $4-cost with Alms anyway, only to end up buying an Alms to gain nothing on your turn.