The flowers are always going to win out in our garden, but I do recall using dried day lily buds bought at an Asian market in hot and sour soup, and as I recall, they had a very nice flavor, mild but slightly tart.
The flower that would be endangered if I could persuade Mr. H to make space for it in the garden would be nasturtiums. My mother and I picked some to put in salad years ago, and after that it was always a contest between flowers and food. Kind of a peppery taste, like a mild watercress, IIRC, and of course, beautiful in a salad.