I don't think you have a goldmine but i do think artsdepartment.com is fine. All arts are generally grouped together due to fiscal restraint, thus the plural is prefferred. With such breadth of coverage you may want to consider keeping it and developing it yourself.
SchoolsOfArt.com is OK but I see no potential for resale. I'd make a directory listing of art schools and use it to promote your commercial art site(s).
(Edited typo)