That said, I agree with Warped, Batman Begins is a enjoyable film, despite the inclusions of Ra's Al Ghul (a character I've never liked), and Rachel Dawes, a pointless addition that I still think should have been Vicki Vale.
I don't see how Vicki would've worked in that context. The character needed to be a childhood friend of Bruce's, someone who'd known him from the beginning, someone he trusted so much that holding onto her respect meant more to him than avenging his parents' murder. The character also needed to be a district attorney, the one idealist within a corrupt justice system. She was far from pointless, since Bruce would never have become Batman if she hadn't steered him away from vengeance toward justice. She was the embodiment of (or at least the spokesperson for) everything Batman fights for, the ideals that make him a hero rather than a psycho vigilante.
If any pre-existing character could've filled Rachel's role, it would've been Harvey Dent, not Vicki Vale. But obviously they felt the film needed a love interest.