I'm always going to wonder how different these guys would sound with a male singer. It's not that I dislike Hayley's voice, its just a curiosity I can't get over.
Musically much of Brand New Eyes reminds me quite a bit of the Phantoms by Acceptance. Listen to the intro of Looking Up and then imagine instead of Hayley, Jason Vena comes in with that sexy voice of his. Honestly I quite enjoy the musicianship of Paramore. Obviously they aren't are the most technical group around, but sometimes simplicity can go a long way. Besides, Misery Business is good fun to jam out on guitar.
They would end up sounding much more of what is typical of 2009's pop music.