Has anyone visited Casteluccio? Would the wildflowers in the area still be in bloom in late August?
No wildflowers then, but go anyway. The town itself is not especially attractive, but the landscape is incredible. It sits on the edge of an ancient volcanic crater that is now a gigantic plain surrounded by a rim of hills. Great hiking in the Park of the Sibillini, and Norcia is a pleasant place. Plus you get to bring back the world's best lentils as a souvenir.
If you are driving there from the Spoleto area then Valle di Nera is worth a visit. Locanda di Cacio Re is a great place for lunch.