A little while back, in discussing revision, I noted that some authors believe that revision removes an author's voice from the work. First I called BS, then I noted that removal of one's voice isn't always a bad thing. Like so much in fiction, it can be good or bad, depending on your intentions and your awareness of it (that's why people say it's important to know the rules. Breaking rules is easy, as long as you're aware of what you're doing so you know how to compensate for it).
Personally, when I write, what gets me through the first draft is discovery. That's why I rarely plan far ahead. What I've come to realize is that the discovery that excites me most is the discovery of my characters. And for me, even when I'm writing in third person, one of the best ways to convey character is through the language. Vocabulary, phrase length, rhythm–it shows the reader so much about your character.
And it's fun. I don't get into over-the-top dialect too often. I usually think vocabulary is enough without resorting to a bunch of phonetic spelling or replacement of letters with apostrophes. It's still a lot of fun. I was told not too long ago from a person who read Psychomancer after reading Burden Kansas that they couldn't believe the same writer wrote both pieces. I don't think it was a compliment, but I'm going to take it as one.
I have tendencies, and if you read enough of my work, you get to know my specific vocabulary, imagery I've come up with that I think is good enough to reuse, and just other signs of my own voice. But when I revise, I usually revise to minimize those things, and replace them with the voice of the character.
But but but! I want to be clear here: that's me. I can't imagine trying to hone a consistent voice, but I sure as hell am glad that some other writers have. A number of my very favorite writers have strong voices. Cormac McCarthy and Chuck Palahniuk are two. The result is that their protagonists all come off as being very similar, but it doesn't stop me from loving, reading and then re-reading their work. Kurt Vonnegut is another, though the effect of his strong voice is to make the narrator a character in its own right. In fact, you feel strongly that that narrator character is Kurt Vonnegut, and Breakfast of Champions seems to confirm that fact, since he is in fact present as a first-person narrator in the novel, watching events unfold as the worlds he's created collide.
So I guess, like usual, I'm advocating that you do what you want, and that the best way to be successful is to understand the effect you want to have and carefully consider how to achieve it.
Could that message be any more vague? I can't help it. I'm a naturally ambivalent person.