I was thinking I'd give up on removing the antenna, but I like Rishar's idea, especially if it improves HD radio reception. For some reason it comes in very poorly on the Prius compared to the in-window antenna on the Camry.
I was also thinking of changing the antenna shape to be more teardrop, but I find it interesting that the "separating plate" has less drag than the "streamline profile".
This morning I removed the rear wiper and motor. I have not used it a single time, even in a downpour. The window sheds water well enough to see approaching vehicles, and besides, the people behind need to mind me, not the other way around. The Prius has a backup camera, too, making it less important to have rearward visibility. I've also got pipe insulation blocking 100% of the lower grill.