Scott, We don't know what the quality of a "voice" will be, however we have indications to go on; a) The last aboriginal voice was ATSIC. Both liberal and labour agreed wit should be abolished. b) a constitutionally protected group wouldn't have the discipline of being able to be abolished. c) Already there is considerable debate between aboriginal groups on whether to even have it.
It seems a folly to me to create something that can't be undone when the previous manifestation was agreed by all to be a disaster.
In any case I am philosophically opposed to any race differentiation in the constitution.