If your dining room is hardwood, adding strips of drywall with green glue under the subfloor will make a big difference, do two layers. PM Snickers1 he was the last one I remember doing this at his place.
I put two layers of 5/8" drywall in a GG sandwich between my floor joists. I noticed a very large improvement, and I have carpet on the floor above me. I can't imagine not doing it with hardwood upstairs. It's a bit of work, as each joist cavity varies a bit, but it's not crucial to seal the joists; you're really just adding mass to absorb the footfalls.