I think it would make him stronger with human like emotions. The way we feel blood-lust , feel for the revenge unlocks our potential. Nero hasn't really had his parents killed (actually it's unkown) so he had nothing to put a mental barrier around like Dante's barrier to hide the pain of the death of his mother.
I think Nero is a version of Dante or Virgil , if they grew up properly.
They are half human after all. plus Capcom would want to keep the plot simple so things like claiming Nero's a remenant of Dante is bab.
oh yeah , Metal doesn't carry DNA or blood so thats the theory out of the way.
Nero's just a more human Dante , a person with emotions , a desire to protect Kyrie and people , and as Dante Aseroth stated , A demon's power increases when there protecting people.
there , my mind hurts now. =]