There's a fine line to walk, but the width of that line depends on your goals. If you want to just write marketable stuff without a damn for your passions, you can be a category romance or formula fantasy writer, churning out bodice busters and Forgotten Realms tomes at a rate of two every other year. If you want to be the Artiste (note the capital A) who writes with passion and concern without a damn for marketability, then accept that you'll be a starving writer living in a loft cursing the fools who are too small-minded to understand your vision.

So maybe the trick is to balance passion with marketability. Sometimes you have to make artistic compromises; A. C. Crispin mentioned having to move chapters around in her book Storms of Destiny to start the novel with a male lead instead of a female lead, in order to improve the novel's chances of selling. So how much of your vision are you willing to compromise in order to make your vision known? Hmm. Just thinking out loud here.