I have the iPad 4 (provided by the company) and bought a private iPad Mini in addition after trying one in a shop.
I actually use them both, but for different things. I mainly read magazines, newsfeeds and books, and do my email on the Mini. For Web surfing, document review and "advanced" apps (like iThoughts HD, OmniGraffle, OmniPlan, Pages, Keynote), I highly prefer the iPad 4 (well, an iPad 3 would do as well, I do not really see a benefit from the iPad 4 when using any of them, except when zooming in on huge PDFs).
With any of the advanced apps mentioned above, I can clearly see what Jobs meant when he talked about fingers being too big for a smaller screen size. My input errors with these apps increase tremendously on the Mini, to a point where the usability becomes un-Apple-like.
The only real benefit of the Mini is the weight, the size of the bigger iPad does not bother me, I actually prefer it. So, in the end, I am much more interested in a lighter big iPad, than in a Retina Mini. Even a Retina Mini will not make my fingers a better match. I do not really see developers optimizing apps for a third screen size (at least no developer of the apps I am using has made such an effort so far).