The best stretch of Ellie Parker hits early, as the title character, a struggling actress played by Naomi Watts, motors from one tryout to another, changing clothes in transit and seamlessly blending the bad comedy of her own life with the bad drama she’s auditioning for. Watts, whose memorable audition scene in Mulholland Drive launched her into stardom, makes a glorious mess of herself playing her karmic opposite. Her daily challenges (”Let’s see who can cry first,” she goads a fellow thesp) carry existentially low stakes — success isn’t just distant, it’s inconceivable. See, Ellie’s determined to Be Someone in Particular, a tall order for someone whose ”career” is based on her tendency toward nonspecificity. But the movie suffers from a similar dilemma. Writer-director-costar Scott Coffey, a tart comic mind who should cast his net farther from the 405, pads his story with more and more familiar degradations, and Watts plays each one to the hilt. (The Chevy Chase cameo is priceless.) But he can’t disguise the flick’s origins as a cynical Sundance short. Showbiz self-loathing is trading up with Extras and Entourage, but it’s still best administered in TV-size drams.