I think I'll probably pick up the iPad Mini because I read a lot of textbooks for school. I was considering the full size but I tried out the Mini in the store and the screen is actually quite large. It doesn't at all feel like it's in the same class as the Nexus 7 or Kindle Fire.
I think if your primary use for a tablet is gaming, videos, remote desktop, opening apps, reading novels and stuff like that, then it's fair to compare them. But if you're going off of actual screen size and whether or not science textbooks are readable, I would say the Mini is in its own class. I would prefer the Nexus 7 but the super wide screen is just not friendly to my uses. I'll probably pick up a Novo 7 Flame 2 for my gaming/high tech uses and the Mini will exclusively be for reading textbooks. Then again, I might just pick up a used iPad 2 for $250, save money, get the full size screen and call it a day.
But for anyone who prefers new, it's something to keep in mind that the iPad Mini is definitely larger. It would also be quite awkward to try to slide into a pocket. If you want something you can one hand, slide into a pocket or something, avoid the Mini.
All in all, I would say a spec sheet is nice but try to get into the store and play with display devices before you decide. There is a definite difference between what you see in an Engadget review and what the device actually feels like when you use it.