If you don't already have a GNex, definitely get the N4.
IMO, the only 3 reasons I can see not getting the N4 are
1) if you can't charge your phone much due to constant travel and need to carry extra batteries,
2) it's not enough better than the GNex (if you have one) to spend that kind of money; unless, of course, money's no object for you or you can sell your GNex at a high enough price to offset, and
3) if money is an object and you can find a GNex for less than $150-$200.
Unfortunately (and fortunately as far as money goes), I already have a GNex (that is waiting for me at home after being repaired by Samsung, but that's another story) that's less than 3 months old and I still love it (if it works like it should when I get it back tonight), so as much as I want the N4, it's hard for me to justify the expense.
If it breaks again, N4 for me!