What's With Mars?
I think that making use of the Veela ancestry is a good idea, although the 1/8 is a slight setback.
I'm not sure how you would work out the amplifying, but I wonder if it would be realistic. Would she use a spell or take a potion, or is it an innate skill like Metamophmagi are born with?
The pride I completely get. Look at her parents: Fleur, former TriWizard BeauxBatons Champion. Weasley, Bill. You don't get more stubborn and proud than a Weasley, and add Fleur, well, need I say more? (actually I probably do, but I can't think of the right words right now).
Her looks seem fine, except maybe the chubby from spoiling. Curvy, ok, she's part Veela, but she has 2 siblings, which usually means less spoiling. She also seems a tiny bit too nice, but if you introduce and play around with some flaws she will become less Mary-Sue (from what I think you mean anyway)
Gryffindor and a little bit lazy also seems reasonably in character (if I can call it that), as she can always charm some of the male professors at least into giving her decent marks...not something I'm suggesting she does (pride and all) but if she really needed to, I'm sure she would.
So I think that everything here seems fine except the control of this amazing Veela enhancing ability and the possibility of turning a canon character into a Mary-Sue. Good luck with controlling the bunny!
Snape Hates Me
I think I would make the amplifying an innate skill. I don't think I worded it very well though. It's more like she becomes more noticeably Veela at some points. Sometimes it's a conscious decision and takes some effort, but other times it just happens, maybe because of powerful positive emotions. I think people generally look better when they are happy, and it's a similar thing here. Does the idea still sound totally implausible?
Part of why I chose to give her slight weight issues was to tone down the Mary-Sueness by giving her a physical flaw. In my head, she is something of a daddy's girl, and so Bill isn't very good at saying no to her. She is his first child after all. Also, she is the first Weasley grandchild, so I think Molly's love of cooking might have had an effect on her. I have always wondered why more wizards aren't overweight, given the apparent stodginess of Hogwarts food (at Harry's first meal at Hogwarts, most of the food mentioned seems to be meat and carbs). However, I digress.
As for personality flaws, I think she could be quite self-conscious at times, and also sometimes quick-tempered and impulsive. I do want her to be a nice person, as she grows up in such a lovely family, but you're right; I need to find a balance between nice and Mary-Sue. Does this make her sound a bit more realistic?
What's With Mars?
This is sounding far more plausible now. I'm not really sure what can add...
Victoire could be a daddy's girl, and that does give a reason behind the weight issue. However, I think that the Weasley cooking is much better as it is a well-embedded fact that Weasleys love their food, and Molly is a wonderful cook.
On your digression, I must mention that they often wear robes, which perhaps hide this.
With the personality flaws, I think that self-conscious is good, because she will have people looking at her what with her Veela heritage, her mother, her father, her relatives. The impulsiveness and quick temper are, I think, Weasley traits already. She has been described in this thread already as strong-willed, so perhaps she is stubborn - both a flaw and sometimes a strength. She is beginning to sound a little less Mary-Sue now though, which is always good.
I suggest that perhaps you check out Bill's and Fleur's threads or Wikis. I'm not entirely sure how helpful they'll be, having not read any of them myself, and I know that children are not clones of their parents, but they might be useful: you never know.
I agree that she may be reckless and brave, even a little rebellious, but I can imagine her with some similarities to Fleur. I don't think she's snobby or elegant, but she would be very proud and have a quick temper. She's probably very 'Weasley', a lot like bill and charlie.
In the Rubble at Godric's Hollow
Searching for Neville's Toad
I expect she'd be a Ravenclaw.
Amazing Avvie by Nadia and Beautiful Banner by BP!
Kill the Spare
Th trouble with this statement that she'd be a 'proper Weasley' is that the Weasleys aren't one amorphous lump with one personality, but a disparate family with many distinct features.
Bill - Bright, dependable, adveturous, glamorous, stubborn.
Charlie - sporty, brave, leaves home for another country.
Percy - Bright, uptight, rule abiding, not a huge sense of humour, repressive, stubborn, brave
Fred - Bright but doesn't care about it, lazy unless he gives a damn about a subject, smart, slightly cruel streak, stubborn, brave, loyal.
George - ditto, but he's slightly kinder in my opinion (he's the one who notices Harry needs help with his case)
Ron - loyal, usually dependable, jealous, tactless, dry.
Ginny - feisty, sporty, smart, not made a prefect, opinionated, jealous, brave, irritable.
So, saying Victoire is a proper Weasley is actually very hard to define.
Also, you shouldn't dismiss Fleur's own qualities and influence on Victoire.
Very brave, very loyal, smart, fearless, as well as the glamour she possesses. She and Bill are well matched.