I think having a unique voice is a big plus, assuming it's "good" unique. It can also be a hinderance in certain circumstances and it all depends on what you want and how you go about achieving it. For example: let's say you have a lot of songs you've written/produced and you send them off. A label is stricken by the uniqueness of your vocals but doesn't care whatsoever about your actual songs. They may give you a call with the intentions of you scrapping all your material for other material they have lying in wait. If you don't mind what it is you sing, or if any of your songs are ever used, it could be great. But, if you actually have intentions for YOUR songs you can kiss them goodbye as people will become familiar with your voice attached to the songs you were made to sing. When you try your own stuff, 9 times out of 10, they won't want it. Oddly, Leiff Garrett comes to mind. He struggled mightily with wanting to do his own tunes and not being able to. That of course is only one scenario. If you're as good as those you mentioned with not only a unique voice but great songs it could be a win win. A positive outlook is definitely needed as well as a strong, strong work ethic, determination and a willingness to fail on your path to getting what you want out of what you're doing.