I would consider vocals an important compositional element that are no more or less relevant than the function of other instruments within the composition. It really comes down to what the spirit of the composition requires.
Mastery of composition, using the form to convey that spirit, is probably the one universal thing that makes an album great. By that reasoning, you will find all great works have a unique voice and a vocal style all of their own.
The vocals on early Burzum, for example, are in perfect compliment of the written material, production aesthetic and above all underlying spirit of the work. To have Craig Pillard re-record the vocal track would surely sound interesting, but would probably miss that spirit.
In my opinion, Burzum - From the depths of Darkness also missed the spirit as did that early compilation of Darkthrone covers.
I might also add Eliahu Inbal conducting anything by Bruckner.