For me an iPad is not a computer substitute.
Said so, I enjoy my iPad mini to take quick notes at college, play some games, media consumption when traveling, etc...
With the iPad it was either my MBP or the iPad. In most cases that would be good news, but not for me, since the iPad is so limited that I couldn't afford to leave my MBP behind.
With the mini I can take it everywhere, exploiting what an iPad makes best, while not compromising the flexibility of a full fledged computer (my MBP).
Nonetheless if the full-sized iPad gets the same weight and thickness of the mini, then it is a no brainer for me.