The differences between how you subjectively, mentally perceive red (your red "quale") and how I subjectively, mentally perceive red (my red "quale") might not be interesting, or determinable, or even meaningful. But what about how you perceive red and how I perceive sweet? That difference is hard to dismiss.
Your conclusion that "'red' is the property of looking red to normally sighted humans," I'm all over that.
In addition to allowing me to use the concept that we name "sweet" and rewarding me for eating sweet foods (so that the human animal in the wild favors sugary foods), why is the recognizably distinct mental state that I associate with sugar sweet? Why isn't it red? Those two sensations are non-trivially distinct, even if your "red" and my "red" are only trivially distinct.
I can sort of wave my hands over reversed-spectrum hypotheticals, and the difference (or lack thereof) between my "red" and yours. Variations within a sense can be imagined to be indiscernable and meaningless. But differences between senses are harder to dismiss.So I come back to your reading of Dennett, that "Red is 'red' simply because that is what it is like to perceive a red object." This leads to the question of why is it like "this" to perceive a red object and like "that" to perceive a sweet one. My guess is that the answer will be explicable once neuroscience has advanced. I think of Dennett as like Darwin, someone who propounded a sound theory before scientific knowledge was advanced enough to support it. Darwin's concept of heredity by blood actually didn't work, and not until scientists discovered genes did natural selection make sense. Likewise, I think, some day it will be clear why the "red" quale and the "sweet" quale are different neurologically, just as it's now clear how light waves and sugar molecules interact with the cones in the retina and taste buds on the tongue.