My approach on the mash pH is to get it into the 5.2 to 5.4 range because [supposedly] this is the optimal range for mash activity (enzymatic, conversion, whatever). I think that the efficiency or effectiveness of your mash could suffer if the pH was too high or low but I don't know if that issue or the issue of fluctuation would impact beer flavor. The addition of sparge water that is too high in pH or the boiling of the wort when the wort pH is approaching 6.0 would have a much bigger impact on color, clarity and flavor of the finished beer than a slightly off mash pH or fluctuating mash pH. All that said, my strategy is to add CaCl or CaSO4 and lactic acid to my mash water as it's heating. What is added and how much depends on style, Bru'N'Water, the SRM of the beer and personal experience. This way, when everything in the mash is mixed together, adjustments are either small or not necessary at all. I also spike my sparge water (which starts around 7.5 pH) with 1.5 to 2ml of lactic acid as it's heating so I can bring it down to around 5.5 pH when it's added to the MT.