D.H. Lawrence says that myths are "inexhaustible" because they are symbols of heart mysteries. That is, they can't be exhausted - they somehow have embodied some central human mystery (love, loss, being a body in time, who knows which or what?) and thus can be retold infinitely and still be rich. That's part of your saying: it's old, but it's also new. Or: there's nothing "new" in the human heart, but it still matters lots.