I am no expert, but if the frets and the nut were made of cheese, it would sound terrible. if they were made from plastic, yes, terrible.
Sound travels best through a dense and rigid material, increasing sustain. Metal therefore is ideal.
To me, it stands to reason that a brass nut would improve sustain over a bone, composite or plastic nut.
But to a noticeable degree? Is the guy in the audience going to faint in awe at the improvement a brass nut has made to your bands sound? Doubtful.
Looks awesome though!