There are people who get really into decorating, who (hopefully) have the storage space to keep things, who probably hit up the clearance deals after all the holidays, but I can't imagine it's lots of people, especially for a more minor holiday like Valentine's that isn't usually very decorating-heavy the way Christmas or Halloween can be.
We didn't even do boxes for Valentines when I was in school, we just passed them out loose. xD
Edit: ooh but maybe the teachers hit up the clearance, they usually decorate their classrooms out of pocket.