I was raised knowing that ph balance is important (not that I ever achieved it). I read the book Vermont Folk Medicine by Dr. Jarvis when I was a teen and he said that most pathogens only grow in the wrong ph...pathogens of the urinary tract and the digestive tract etc. He listed a whole slew of them that only grew in the wrong ph for our body. He had many examples of the wrong ph causing ill health. That book is still available online as it is sort of a cult classic. Then along came another book called Acid/Alkaline by Herman Aihara. That book said that the basis of the 2 thousand year old diet of macrobiotics is ph balance. Herman applied modern science to the old traditional macrobiotics diet and showed that their food groups corresponded to mineral content of the food and that it is healthiest to eat a balance of acidic and alkaline mineral foods.
The reason you see books with titles like "Alkalize or Die" is NOT because you are supposed to be alkaline but because most people eat too much acid-forming food and so the way to achieve balance is by eating more alkaline food in order to recover health. The ph of the blood is supposed to be something like 7.3 or 7.4, which is slightly alkaline, but the ph of urine is supposed to be somewhat acidic...the ph of the stomach is supposed to be VERY acidic, etc...so ph is different in each part of the body. The easiest to measure at home is the ph of the urine and if it is off, they say the ph or your body is off.
Yes, your body will steal minerals from the tissues to make the blood the right ph, but that is NOT HEALTHY for your tissues! For instance, if your body has to steal magnesium from the heart to make serum magnesium in the blood come out right, you can have a heart attack (and no one will know why because the idiots measure serum magnesium when they look at electrolytes). Etc. (This is not an electrolyte, but I am familiar with how the body steals copper from tissues to put in the blood in the case of inflammation because copper is a poison and your body is trying to save you from a plague, but the result of stealing it from the blood vessels can be a burst aneurism, etc). So saying you are acidic or alkaline does not refer to your blood ph, but it is meant to refer to whole body ph and since that cannot readily be measured, what is tested is urinary ph.
That said, if you have a VDR (Vitamin D Receptor) genetic defect like I do you will NEVER get your ph right by diet and ONLY by large dose Vitamin D supplements. In fact, there was a website (I long since lost) of people who simply administered Vitamin D until the urinary ph came right...they did not address this via diet at all.