So as many have commented, water pH is almost irrelevant, so adding the 'salts' is for trace minerals and flavor. (But not 'flavor' as you get from salt in pasta; it's more subtle and more associated with chemical reactions than brute flavor force).
I say the key is having 1. Enough minerals to allow the mash to do its thing, chemically and 2. The Chloride/Sulphate ratio desired for the beer type and taste preferences. Most styles have profiles in the water calculator; Palmer also gives useful water profile information in How To Brew.
In my water, which is very low mineral (Yay!), I almost always start with Gypsum (Calcium Sulphate), the goal being to add some Calcium and all the Sulphate I need. Then I add Calcium Chloride, to finish off the Calcium levels and add the Chloride level I need. I will then add some Phosphoric Acid it the Ph is too high. Typical quantities are 3 grams of each (in 8 gallons water), but it varies.
I do have Epson Salt (Make sure it's the unscented kind!!) to add Sulphate (Magnesium levels rarely need to be more than 10 PPM, but can be much higher) and table sale (non-iodized, like Kosher salt) to add Chloride. I try to keep Sodium levels below 100. I also have food-grade Lye (NaOH, also great for pretzels) and baking soda to increase pH when brewing with really dark malts. Other chemicals can be used, but carefully consider your goal to avoid having to stock all sorts of powders, and eye of newt.
Using the scientific method, the ideal situation would be to brew two batches, one with salts and one without, ferment and package them identically, and see if you can taste the difference.
