Re: Knee sleeves
I had Tommy Konos and would replace them when they started to tear. TKs were somewhat known for doing that. Mine would last about a year. Have some nordic somethings now. Should be more durable. I expect they'll last several years, like Brad said.
I rinse my sleeves in tap water right after taking them off and let them air dry. I don't do anything else to clean or maintain them. Have never had any issue with smell.