“Bah, humbug!” It’s not a cliche; it’s a lifeline. The words from Charles Dickens’ “A Christmas Carol” are worth their weight in counting-house gold to local theater companies this time of year. As is the graceful familiarity of “The Nutcracker.” The uplifting notes of Handel’s “Messiah” too. These holiday touchstones aren’t lost just to audiences this year. They’re lost to small arts groups that rely on the bountiful revenue to refill depleted end-of-the-year coffers. But more than that, leaders said, these shows deliver so many intangibles — sowing company camaraderie, strengthening ties to core audiences and attracting new fans for the coming year.