A few thing I think would go over well...
1. An Ant-Man helmet - both retro and modern.
2. A wolverine mask. Mofos love wolverine.
3. Wonder Woman "armor" - the WW on the chest, the tiara and belt.
4. Hawkman/Hawkwoman wings
5. Spider-Man face shell (perhaps with moving jaw?)
6. Generic muscle suit in pieces - ok. I know this sounds crazy, but hear me out. If you pepped a chest as a shell and maybe back you could wear that under a suit. Maybe you don't need the chest, but instead the arms or the thighs or calves. Who among us has heroic calves? Sure it could be done with foam or padding, but some people don't feel comfortable with those. And who knows, someone could use the pep as a mold for cold-casting foam.
I don't personally need any of these. Just some thoughts.