I think it was Townes Van Zandt who said, "There's two types of songs: the blues and zippity doo dah." And also a reply to a heckler who asked if he didn't know any happy songs: "Ma'am, these ARE happy songs."

I've written a happy song or two myself (but always with an element of, or in response to, some sort of pain or tragedy to kind of ground them), but I think Art's on to something there. The ones that really hit home aren't too glib.