I really don't think being nasty means anything these days, except perhaps a greater propensity to get a yellow/red card.
Who do you know that's "nasty" and actually uses that in some way that can't be done without the "nasty"?
You want aggressive carriers, but we have that. You want people who hit hard in the tackle, again, we have that. We want a powerful scrum, we've actually been doing rather well there (especially with West). Maul defence has been pretty good, except for Rowlands, who either smashes them, or gives away a penalty, which is problematic.