What do you do with a daffodil plant after the bloom has expired? Cut it down? fold over the leaves and rubber-band them?

Leave them be and let the foliage die back on their own. Letting the foliage do that feeds the plant for next year's blooms.

I experimented with that. I have bunches of King Alfred (or is it Alford?) daffs on the north side of my barn in two large clumps. Same exposure, same dirt. One side I cut down to about 3-4" after bloom, and the other side I let die it's usual ugly death. The following spring, I could tell no difference between the two. Both returned fine, and I didn't notice any difference in the blooms. I do have various plants that cover the spent foliage, but no longer worry about the cut-or-not question. Sometimes I want a neater look, other times I don't really care. Do as you please is my advice.