It all depends on the amount of traffic the domains get. Plus on top of that you will not know if they will make you money unless you park them. Some domains get hundreds of visits but without clicks. Some get 10 visits a month but get 7 clicks and make $10. It just all depends on the quality of traffic your domains are getting.
Go sign up at Namedrive.com or Sedo.com and park your domains. Do this for a week or however long you want. I do suggest you park your domains if you are not using them or have no plans of development. Who knows they might get sudden traffic