This question (dust cover or no dust cover) comes up every 6 months or so. It is quite likely that, if SQ is the sole determinant of what to do, each person must listen and decide for his or her self. Because first of all there are differences in how different turntables mount the dust cover, which has an effect on resonance and energy dissipation, and two, each of us is limited to one pair of ears, one brain, and one set of biases.
I cover the platter when my TTs are not in use, sometimes with a piece of cloth, taking a cue from the Kenwood L07D, which came with a lucite cover in the shape of an LP; it has a hole in the center for the spindle, over which hole is a convenient metal handle. They made no attempt to design a conventional "dust cover" that would cover the platter and tonearm during play. With all the millions of accessories that various companies try to sell us, I am rather surprised that no one makes such a "platter cover" for the aftermarket.