I think the costumes should represent the different types of characters and powers in the movie.
For example Batman has the Bat suit, SWAT type battle armor. And since he is human he has a very man made looking suit, and a suit made to protect his body. It is gritty looking, and dark.
But Green Lantern's costume is a very alien looking police uniform that looks very alien and looks like it came from his imagination (no seems, zippers, buttons, belts or any of the sort.) His costume should be very bright, and sometimes glow, and look very sci fi and spacy.
I think the film, in my mind at the moment, seems to be about 6-7 very powerful superheroe who usually work alone, who come together and form the greatest superhero team in the world.
The film should embrace and maybe emphisise their different backgrounds, characters, powers, and costumes.
Maybe have a different design team on each costume (at first) to make each costume seem like they came from entirely different worlds. (while still looking like they are from one world and still look like their comic personas.)