One thing I have never agreed with and will never agree with is the typical X-Men fan mentality that a character's worth is measured by how much damage that character's powers can cause. One of the prominent themes of the X-Men franchise is what a person does with his or her power(s). The comics, cartoons, and movies have pointed out time and again the folly of assuming that everything about a person can be summed up by a specific attribute, yet on message boards I see post after post of X-Men fans making the same assumption.
Does Rogue need to absorb Carol Danvers' powers in order to be a useful character? I doubt it, because not only does it detract from her primary power, but it would also mean that Rogue's value as a character is her ability to fly and hit things. I'd argue that she should have an identity over and above what she can do with her powers. Granted, her powers definitely shape the way she thinks and the way she lives her life, but shouldn't dominate everything about the character; if her powers were removed somehow, it shouldn't lead to Rogue losing her entire personality.
Regarding the personality, I admit that it took me quite some time to get used to Rogue as she was portrayed in the first movie. I'd grown up with the tougher, more free-spirited Rogue seen in the comics and movies, so I had a hard time getting used to someone who was a lot quieter and who acted like a typical teen runaway. It wasn't until Rogue's last scene in the movie, where she dressed a lot sexier and seemed to come out of her shell a bit, that I understood what they were doing with the character: they were showing Point A and a few other subsequent letters in Rogue's journey instead of starting with Point Q as the '90s cartoon did. When Rogue arrived at Xavier's doorstep in the comics, she'd had a difficult time with her powers and didn't have much in the way of self-confidence. In X2, her character growth continued, and she developed some more with a character arc that had less to do with ho many butts she could kick and more to do with how she handles dating like a normal teenager when getting close to her boyfriend is problematic. I'm not sure what direction X3 will take her, but I would definitely feel cheated if the only character development she gets involves what powers she gets. I will admit, though, that one of the things that attracted me to Rogue in the comics and in the cartoon was that she was a complete tomboy in terms of her behavior. She had a temper and she didn't mind getting her hands dirty. Movieverse Rogue doesn't have that quality, but I'm not about to declare her useless because of it.
I'm not sure I agree with the idea that Rogue immediately became a light-hearted sexpot immediately upon being drawn by Jim Lee. While I don't have a lot of comics from that era, I have quite a few from subsequent eras and I'm actually hard-pressed to find an issue where she stays in a good mood for the duration of the story. Sure, there are a lot of light-hearted moments where Rogue jokes with her teammates, but that looks to me like the result of living under the same roof with these people and considering them her family. I think she'd have a hard time living with the X-Men and remain the same character she was when she left the Brotherhood; each team would bring out a different side of her personality. And I can't help but liken her relationship with the X-Men to being at a burn camp in a way: she's around people like her who have a similar affliction and who accept her and allow her to be more okay with who and what she is than she was before. Pretty soon, being around her normalizes her experience to point that she isn't as cursed by her mutation and she can relax. The '90s cartoon version was the most upbeat version of Rogue I've seen (and even then she had a lot of sad/dark moments throughout the series), but it would have been out of place in the X-Men movie context unless they established her as being an X-Woman for years.
Would I like to see her adopt Ms. Marvel's powers in a sequel? I guess, but I could live without it. Years ago I'd have had a different answer, but these days I realize that her basic absorption power presents possibilities that Ms. Marvel's powers don't. Does it make her as much of a hardline fighter? No, but that means she has to work harder in a battle and approach tactics in a different way. It shouldn't be too much of a problem if the X-Men act like a team and watch one another's backs.
Actually, it would be interesting if she ended up permanently manifesting some other power besides Danvers'. After X1 I thought it might be interesting if she'd retained at least a tiny bit of Magneto's power or Wolverine's healing factor. But I don't see it as completely necessary to the character. I ultimately think it's erroneous to think that a character would only be interesting or useful if only she were on a higher power level. That's not very effective in exploring the character herself, and it would miss the point by a fairly wide margin.