The galley washdown is almost NEVER used. Unless you're offshore or really conserving water because of tankage or supply issues. The galley saltwater is off of a footpump.

The washdowns (from the anchor locker) are a different story. There, we don't use the fresh water very much. That's because to clean our all-chain anchor rhode, it just takes to much water in the Chesapeake's mud. It really would be good idea if fresh water weren't an issue, because there would less salt in the anchor/forward sail locker ;^).

I would NOT valve on spigot for both fresh and salt water for a whole bunch of sanitary and maintence issues.