There is nothing called a 'bad' theory and no theory, howsoever wrong or disproved they later become, can be called far from valuable or a waste of time. For, every theory becomes a part of the maze; yet another intriguing additional pathway in the maze of human quest for the truth. Only certain routes of this maze lead us to the real. The others did mislead us for a long while, apparently seeming to waste precious time and resources. However, in the process, they stretched the boundaries of human imagination and took us to new places, sights and paved way for innovations yet to come.
Nothing revolutionary ever sprang from a single mind's work from scratch. We all stand on the shoulders of those who failed. We all carry over the efforts of those who stopped. To take complete claim over greatness is a folly of the greatest order.
Without knowing it... without realizing it, we all borrow from and owe to the great collective conscious.