I think it's fair to say that for all writers, the importance of being published is only usurped by the importance of having a solid backlist. The backlist is the collection of other books you've written that will keep growing with each new book you publish. Writing and publishing your book is only one small part of the overall equation; getting an impartial third-party to review it - while near miraculous - is yet another small part; building book buzz is a HUGE part and finally, making sales is the final part of the equation. If you've managed to get all of that, you think you've finally made it, right? Wrong...
Even if your book is lucky enough to have had some sales, the only way to see a momentum build is by keeping the fan base you've managed to capture and then build on it...and fast. Once a reader has read your book, and they liked it, they'll want to read another one and if there isn't one to read, they'll look for another book by another author. If that reader really, really liked your first book and remembers to think of you six months down the road when your next book becomes available, you're pretty lucky. Most readers have a much shorter memory span and want instant reading gratification - and quite frankly, they don't have far to look. There's thousands upon thousands of titles and authors to choose from, merely with a few clicks of the old mouseroo.
In past years, traditional publishers have encouraged authors who like to write in more than one genre to do so under a pseudonym, since readers of one genre would become "confused" by an author's backlist comprising of more than one genre and that they'd be less likely to remain loyal to that author. Some authors, like Nora Roberts and Stephen King, have written under pseudonyms for different series of books. I personally don't buy into the whole "confusion" argument. However, I think that any author that writes in more than one genre will still have to develop a reader base, regardless of the genre. I also think that readers today are more open to reading different genres of books by the same author, thanks in part to the wide appeal of cross-over books like the HARRY POTTER series and the TWILIGHT series. Some authors, like Karen McQuestion, have a backlist made up of more than one genre of books and by the looks of things, this diversification has only served to enhance her fan base and her reputation as a talented author.
So I guess the moral of this little blog is...write well...write often...and death by diversification be damned!