(it's all assumed bad until proven otherwise).
I'm not a fan of the Romantic poetry either, from my Very Subjective Point of View most of it is very bad and that's exactly the reason why I decided to quote these fragments. It was supposed to be a joke. Of course these are Polish translations, good and adequate ones I must add, and vocative is absolutely necessary here, there's just no other way to render it.
As far as contemporary language goes, there are plenty of usage examples with the words: ziemia, gwiazda, ojczyzna, dom and suchlike and it's not just poetry. Granted, addressing a computer might sound funny... or it might seem so until you've experienced a major system breakdown at the worst possible moment.
OK, maybe I'm splitting hairs. But anyway, even if you limit the vocative case to nouns referring to people, it's still indispensable in the structure of the language at its present stage of development. I know quite a number of Poles who say "poszłem" instead of "poszedłem", but I have yet to meet somebody who would say "pan doktor" instead of "panie doktorze" addressing the physician at a medical examination. You can't substitute Vocative with Nominative here, there's not even room for a mistake. So maybe Nominative will completely replace Vocative at some point in future, but it's still a long, long way to go.