A) No, it doesn't do that magic. Law of conservation of mass would have something to say about that. The plant cannot manifest building blocks out of the ether. Flushing is a culturally-constructed concept. Someone did it a while back and said it was best. It somehow stuck. This is the problem with anecdotal stuff. Ego and lack of a better undertanding of how to figure out causality the primary causes. (not employing the scientific method and just assuming what worked well to the eye is best.)
Flushing does not reduce minerals in flower material. Anyone that says this is simply wrong. We have lab equipment that is more than capable of resolving such things. You can trust the research. "Initial studies" are mostly proven false at a later date, but with such a simple question as this relative to our technological capabilities, you can trust the reults.
B+C) You cannot "water down" your flavor under any reasonable context of common sense gardening. You can evaporate terps off the plant in heat and extreme light, which could impact flavor. Ppl say outdoor vs indoor taste different and maybe some methods of fertilization will impact flavor, but a nuclues or chlorophyll organelle won't change compisition.. ie. the parts of the cell are still made the same and need the same proportional amount of N, C, H, O, et al... to make it. The cooking instructions don't change in the DNA... So, any variance is likely limited in some ways but does occur. A buddy of mine grew a clone. He feeds much differently than i do. It comes out a bit different. So, it can effect proportions of 'something' in the plant.
Blind taste tests show that ppl cannot distinguish between a flushed and non-flushed harvest.
D) Some ppl still cling to it, yes. Some ppl want to use antibiotics for things caused by viruses. conclusion: ppl are not smart.
Flushing is tool you use when the plant is suffering from some sort of toxicity, or may some other condition I just don't have the imagination to think of in this moment. The point is, when it is done for real reasons, it has a real effect. Flushing at end of harvest has no real effect other than the figments in some ppl's minds.
So, if it is healthy, no worries. if it is toxic, give it water... if it fades and timing looks right for bud development to finish, that's senescence and no problem as long as plant can finish its buds. I wouldn't react the 'other' way and feed it more either, assuming a well-balanced diet exists.