I would have loved it if that was how Twilightovampirification worked - whatever you were before the change, it makes you More. More beautiful, More average-looking, More self-centered, More caring, More shy, More violent, etc. Bella as that kind of vampire might become haughty, obsessed with personal appearances and staring into mirrors for hours on end; she might be neurotic, baking manically for three days straight in a desperate effort to buy the affections of someone, anyone who would tell her they appreciate it and thereby prove to her that someone needs her and cares whether she's even there or not....Name one "good" thing and one maybe-not-so-good thing that could come from forcing your three-dimensional personality through a two-dimensional strainer. (Mixed metaphor or just dreadful analogy? You decide!)
I'll start. One major trait of mine is that I stay really busy. The Meyer-Approved version of this would probably be that I'm the one taking care of my vampire family by constantly modifying our clothes to be more "modern", forging our important paperwork, maintaining several "vampire sighting" blogs to spread disinformation and discredit the actual sightings, and generally working myself silly 24 hours a day to make sure that all my in-life plot holes were neatly tied up. (Sample "todo" list: @asap Convince Mike that my sparkling wrist was body glitter. @someday-maybe Learn hypnotism.)
The Dark-Twilight consequences is that I'd get so busy that I "wouldn't have time" to go hunting on schedule with the others (I have to get these passport photos finished!) and I'd probably be prone to snapping and gobbling down the occasional yappy terrier. Those things would be like popcorn for me. So I guess I'm trying to say that my single-minded devotion to Stay Busy At All Costs would probably disconnect me from humanity and lead me to have difficulty managing my vampire-y urges.