I would think it would be a good thing that Gwen's goal in Sins Past is consistent with her characterization (what there is of it) in Lee and Conway's writing. I guess we disagree on how big a difference it makes to have a character who's been batted around for thirty years' worth of "perfect dead girlfriend" stories stand up and say, "No, this is what I want."
One might argue that it's a bit futile because, this being a retcon, Norman killed her anyway -- on the other hand, you could also see it as Norman, business tycoon and supervillain, being threatened enough by a teenage girl that he felt he had to kill her. Which is a way better story than "superhero's girlfriend get's dumped off a bridge."
And no, she wasn't honest, which was one of the "Sins" she was trying to face up to when she died, but I don't think she was all that forthright in the original comics, either, so I can't say I thought it was a huge violation of her character. She's a scared teenage girl who hides something she shouldn't because her dad's died and she doesn't want her boyfriend to leave her; then she grows a spine, and up. (And then she gets murdered for it before she can fix things: the tragedy of Gwen, not the tragedy of Pete.) I can work with that fairly easily.
Back to Marvels, the reason I think it's creepy isn't because I think Phil has romantic intentions towards Gwen, but I do think he's putting her on a pedestal in that grand ol' chivalric tradition. I don't remember exactly the text he uses but there's a lot of implication that she's too pure to live, etc. etc. It's not Phil Sheldon talking about this nice young girl he just met, it's Busiek and Ross, Silver Age fanboys, talking about the quintessential Silver Age Girlfriend, Gwen Stacy. But because, as you said, Gwen acts like a 12-year-old rather than a 20-year-old, there's a very disturbing picture being painted there of what the Silver Age fanboy wants their ideal girlfriend to act like.