The Alltrack vs. [new] Allroad comparison is an interesting one. I do wonder how much better the Allroad's FWD-based "quattro ultra” is than the Alltrack’s 4motion in the real world.
For taller folks, and having sat in both cars, I do think there’s appreciable value in the Allroad’s longer wheelbase and airier-feeling – if only slightly – cabin. And then there's the noticeable power difference - that's worth a good chunk as well.
I think the sweet spot might very well be a used B8.5 Allroad, with its tried-and true ZF 8-speed, “real” torsen quattro, all on a platform that has, if owner reviews are to be believed, had most of its kinks ironed out.