I would say that 80% of creating good brewing water is reducing the residual alkalinity for most people (I assume most people have hard water in the US). I think that alone will help make better beer. I'd say the other 20% is futzing with the mineral levels.
I have hard water. I still have to add gypsum to my hoppy beers to really make the flavor shine. In all cases except for stouts and other beers with high roasted malt content, I acidify the mash/sparge water to reduce the residual alkalinity.
This won't work for everyone, but it will for a lot of municipal water sources in the gulf coast region.
None of the breweries around here that produce any larger quantity of beer futz with their profile any more than I do. They still make great beer.