Comparing the weight is easy. It's the effect of the retina display on the mini that you really need to get a feel for. When I switched from a Nook Color (7" 169ppi) to a Nexus 7 2012 (7" 216 ppi), I found myself not needing to zoom in on stuff all the time. I realized it's not really bigger screen real estate that I needed. It's just the increased resolution. I expect for me, the 7.9" mini 2 will work just as well as bigger iPads while being 30-50% lighter.
Agree that increased resolution does make a big difference. I think I'd still prefer the bigger size, because I can type better with the bigger keyboard, and also my muscle coordination problems make hitting the smaller touch targets on a smaller screen a pain. But for people with no motion control problems this won't be an issue.