Where on your palate are you perceiving the dryness? I perceive astringency forward of my front teeth, just inside the lips. Feels like my teeth have been sucked dry.
Dryness contributors I didn't see mentioned here are roast level and hop bitterness, which I perceive mid-palate and at the back of the mouth, respectively. You might need to back off on one of these.
I don't think 170°F is too hot for batch sparging. The thermal mass of the grain and mash tun are going to reduce the water temperature considerably.
Btw, I've never heard of sparging twice like that. I think what is meant by "roughly half" is that the runoff from the *mash* should be roughly equivalent to the runoff from (only one) sparge.