Ordon Village Link has never been washed, but I never got sweaty in it. It doesn't stink, either so I think it's pretty clean.
Alphonse Elric was cardboard, so that answers that. I did wash the turtleneck and sweatpants I wore underneith.
Davy... I really want to wash him, but I don't know how. I honestly thinking that a garden hose is the way to go. I'm worried that the mask wouldn't dry and start mildewing. The coat is also a conundrum with the seashells, barnacles, and spray paint. I have a hard enough time keeping the barnacles on as it is.
I guess when my cosplay starts to smell or when it gets dirty I wash it if I can.