I have seen this movie twice. While I agree Slater is Hot and all that. But It took Warners 4 years to recover from the critical and financial bomb that was SuperGirl. SuperMan was the final nail in the coffin for the reeves era Superman. IN 1989, Warners Realised rather late in the day that Rather than have a campy looking guy who wears his jocks outside his SuperSuit people wanted something darker and a hero who beat villains up.. Warners Re-invented a much darker hero called Batman.
The Keaton/Burton combination together with Nicholsons demand that he get a gross percentage of the Merchandise of that plus subsequent sequels was a masterstroke and revived not only WB but his own financial clout. Batman Returns made even more money as did Batman Forever and yes even the much reviled Batman and robin. Batman Begins Changed everything.
Because it made sense to bring Bruce back to his origins and the switch to Chicago made the film more real somehow. All filmmakers of Superhero movies are all going to do this. Superman Returns will be different in the sense that he returns to earth after being away for an unspecified period of time. They need to consider carefully about what story to give Supergirl.
Maybe they may do Smallville on her, have her come to earth as a baby. In Smallville, jor el used someone called Kara to tempt Kal-el in coming home. I don't think there was a connection to supergirl there because she was never mentioned again. Look at how much slagging the aquaman debacle has got over the decision to replace one with another. People Will not go to another Mushy romantic film as SG. To fit into the modern time, they will have to make her tougher, harder and dark. Just like they did with Batman.