Well keeping one costume isn't such a bad thing as long as it was a good costume to begin with. But some on...Superman is basic basic basic. He has basic powers, like somebody just made up a man...but super. His costume could have been designed by a five-year-old. Blue spandex, undies on the outside, boots and a belt. Ridiculous.
Now Batman, THERE's are good costume. GREY spandex, undies on the outside, boots, a COOL belt, and a cape with a hood! Yep, totally better.