I know it's one of his classic powers, but I've always found Superman's flying implausible, physically unsound. In the very beginning, he couldn't fly; he could just jump ("leap tall buildings in a single bound"). While I do think Superman has acquired too much power over the years, his power doesn't define him. TV's Smallville has been on for nine years, and Clark has yet to fly on a regular basis.
Superman is more about a strange visitor so admiring humankind that he does everything he can to help and live as one of them. Some may find this aspect of his character too idealistic, but change it and he wouldn't be Superman anymore, and sales would drop even further, not improve.
And if you're interested in my opinion of Wonder Woman's new clothes:
I don't mind Wonder Woman's and other costume changes. Real people don't wear the same fashions they did thirty years ago. Fictional characters shouldn't either, if they want to stay relevant. A change of clothes doesn't change character.