Although I cannot specifically address your Miracle-Mineral-Supplement -related pH question (though it is a good one), I want to applaud you for recognizing the complexity of the pH issue. There is, in fact, tremendous variability throughout specific areas of the body with respect to "optimal pH" and, therefore, this makes for a very confusing and misleading issue. The optimal pH range of the blood is, by the way, between 7.35-7.45 (some say 7.38 and 7.40 is closer to optimal)... Furthermore, the primary means of regulating blood pH is (believe it or not) though breathing. Breathing has the strongest influence over CO2 levels of anything, by far. This isn't to say that other things can't affect pH, but breathing is #1....And too alkaline (too low a level of CO2...known as hypocapnia) can be as damaging and problematic as too low a pH. Optimal pH for the colon is closer to 4. Salivary and urine pH are entirely different, still. Therefore, using pH tapes to measure "body alkalinity" is a bit dubious an exercise, at best. Interestingly, salivary pH values below about 7.2-7.4 can be an indication of essential fatty acid need.
I look forward to other postings on this issue, as I think you raise a legitimate question.