I’ve got to say, I am one of those DM’s who never thinks to include scrolls in treasure hordes. It was an act of conscious will that I remembered to include them in Castle of the Mad Archmage, but they’re really an incredible treasure item for a number of reasons.
First, of course, is their utility in deterring adventurers from using flaming oil. After the first time or two the party finds the charred remains of a scroll case in the debris from the giant spider webs they just torched with such abandon, perhaps they’ll be a bit more circumspect.
Second, they give the DM a controlled way to introduce higher-level spells into the game, as well as giving the players a chance to add spells to their spell books. A 3rd level magic-user can still be a formidable force when he has a scroll with lighting bolt, and it gives players a chance to add to their own spell books without having to find an enemy wizard to loot.
Don’t forget the scrolls!