Navigating the Underdark wilderness if you are not a drow or deep gnome (or use polymorph) is simply a mess.
Also it is extremely easy to lose the sense of direction having 1 room map view, but what is worse, is that you cannot get an idea of the Underdark wilderness and feel how it is structered. You literally grope in the dark.
Now groping in the dark would be okay for a while, and that is what happens if you go there without darkvision, but travelling at least in the Upper Underdark, should be less frustrating in my humble opinion.
I would prefer the 1 room map view being set for everybody in lower sections of the Underdark, where more alien and lovecraftian creatures dwell. In that context groping in the dark would be nicer, again, in my humble opinion.
So I propose to give to everybody the wider map vision in the Underdark.
Drow and deep gnomes would still be advantaged over the surface dwellers, because having 120 darkvision they can see mobs who are further away than two rooms, and thus avoid them more easily. On the other hand everybody would have a more enjoyable time in the Underdark, without reducing the danger in an appreciable manner.
As an added benefit we would see also fewer polymorphed explorers, which are not very beautiful to see for my personal taste.