I use NS on my lone shammy (not a pvp server) for instant heals... it's saved my life so many times in instances and levelling that I wouldn't replace it with the totem of wrath.

For pvp I would prefer the ability to trigger an instant cast lightning bolt/ chain lightning especially if I can use it in conjunction with elemental mastery. (an instant guaranteed crit will make most enemy think twice). I'd also prefer to have an instant big damage spell for when I'm up against a melee (especially if that melee has an interrupt ability).

I'd happily give up totem of wrath just to have that rare occassion where I pop NS and elemental mastery and it procs lightning overload

Now that is from a lone shammy point of view...With five shaman you will probably encounter the lightning overload situation more often.

I think it would be wonderful to get attacked by a few alliance, then have five shamans fire off instant chain lightnings with guaranteed crits.