What does お元気で actually mean? It seems to be used only when people are saying goodbye to one another. Since it is said while parting I do not think it is a question like お元気ですか。 It probably means "be well". Is it short for お元気でください?
Is 気をつけて short for 気をつけてください?
Is 気をつけて short for 気をつけてください?