To be fair, I think everyone who knows anything about X-Men knows that the 'Men' covers the original meaning of the word 'man' (ie, 'mankind'). Fun fact: There was a female member of the X-Men from the very first comic (Jean Grey) and she was probably the most powerful X-Man at the time, too. She was certainly more than capable of sticking up for herself and putting males "in their place".
I suppose they could rename the team retrospectively but I think there are better things that comic book writers can do than rename people. If they went down that road, I would argue that things like "Superman" and "Wonder Woman" should drop the their gender references at all because they shouldn't matter, but that's a whole different kettle of fish...
I do think that Lara Croft is already the female superhero (certainly as much as Batman) that has proved they can be successful. I wasn't a huge fan of the TR movies but you don't get a third movie by being rubbish. Also, Buffy was inspired by a movie, so I would argue that the Buffy movie was so much a success that they did a TV series (as opposed to the other way around), sort of like how Batman/Superman/Avengers stuff has been made into TV series after the success of recent movies.
It's just a case of finding the right story and the right actresses. And hype, I suppose. Marketing plays a big role in this kind of thing.
EDIT: Also, I swear they almost made a Xena movie, I wonder what happened with all that?
EDITRA: Apparently said Xena movie is a possibility that Lucy Lawless is in favour of! You never know!