I am not sure if paint adheres to the fun foam, but I have done my fair share of glittering fun foam and it holds just fine. My first thought is to keep them white, glitter them up with diamond dust, add earring wires and dangle a couple of crystals from the bottom.
You could also very easily link these together to form a fun bracelet. I'm thinking of all the interesting embellishments out there nowadays that could be glued to them.
Any other ideas? I was thinking it would be fun to make a few pairs for friends.