Just thought I'd chime in with my experience. I haven't used the retina mini, but had the original non-retina mini. And yes, I had problems with touch accuracy on the mini. But the pixel density had nothing to do with it. It's just that because the screen is smaller, the touch targets are physically smaller. The retina mini has double the pixel density of the non-retina, but touch targets on both minis are the same physical size. So I expect that touch accuracy would be the same on both. And iPad 1 and 2, which are non-retina, have the same touch accuracy as the iPad 3, 4 and Air. And all the bigger iPads have more touch accuracy than the minis.
That said, I have some physical coordination problems. I think for healthy, able-bodied people, the difference in touch accuracy between the mini and the full-sized iPads shouldn't be an issue.