For all the aesthetics
that Nikki brang (brought?!) I didn't really like her when I found out about her. Paulo was much more likable than Nikki, in my opinion - felt sorry for the guy. But I really don't think it's the actors fault - just plain old poor writing is the reason we couldn't relate to them.
Think about it, why would they introduce new characters now? Each character has his or her own fan base - Paulo and Nikki were NEVER going to have that. In fact, I would have found it slightly insulting had they actually BEEN important. That would have meant the writers needed a Deus Ex Machina to explain everything - which is more bad writing.
But I really don't think they've been influenced into killing them off - I think this was the plan all along - like Arzt. So they didn't have to kill a 'power-character' off. Well, not until the season finale - when we'll surely get a character death, my guess would be Charlie...