I would add, that to my knowledge:
1) You could only treat mash water if you were only concerned with managing mash pH. But for the flavor contributions (depending on style) you need to also treat sparge water too.
2) Brunwater is a great resource. You can use it to enhance your understanding as far as you want to push it. You can also just use to plug 'n chug to get the same optimized results. Just depends how far you want to dive into it.
3) When I first started manipulating my water profile, I bought a pH meter and messed around with it for three batches. I quickly learned that the Brunwater estimates were so close that measuring my pH was not necessary. So I have not used the meter in 5+ years. Though, it does help that I use R.O. water from my own home, so I know what my starting point is more than other, more variable, water sources.
4) Better water = better efficiency, better flavor, better beer, and a better brewing hobby!