It's stupid to argue CN vs non-CN really. CN is clearly better than non-CN. The only bad thing is that you can't start out as good as people with a fixed colour because it's that much harder to lookahead. But when you're at pro level, clearly lookahead doesn't pose a problem anymore as shown by faz/rowe/etc so there really isn't any disadvantage to CN. I'm not saying CN is that much better than non-CN, but if there're no disadvantages and you can save a move or two or get an easy x-cross every 10 solves, it does help.
What would be a better discussion is if it's worthwhile to switch to CN when you're already fast with sticking to one colour, in which case switching to opposite CN is probably the closest you can get to neutrality in solves, because switching to CN will be really, really hard.
edit: So if anyone is just starting to speedcube, the best advice would be to ask him/her to be colour neutral. It really pays off in the end.