Yosemite had to be one of the most difficult places I've found for campers to find a place to shower. I've seen everything from NPS visitor centers (My Rainier) with coin-op showers to reasonable coin-op concession-provided showers (Crater Lake, Lassen). I did have issues with the cost at Lodgepole Village in Sequoia NP being $3.50 for a coin-op shower where you supplied your own towel. That seems excessive.
The showers at Curry Village seem to be enforced now for either a receipt or guest key.
Is there any way there might be coin-op shower rooms installed in the major campgrounds? If they ever plan on rebuilding some of the bathrooms, they could be rebuilt with shower rooms with 24-hour coin-op. Right now it seems to be odd trying to go to Curry Village or Housekeeping Camp in order to get a shower that you may or may not have to pay for.