One thing to consider is that if you buy a second tablet, you will find that most of the apps that you most likely like on your iPad and iPhone are either not available on Android or you need to buy them again. So looking at the iPad mini might make sense for you.
That's what I found out when I got a Kindle Fire in addition to my iPad, iPod and Kindle Keyboard. I would be using the iPad for nighttime reading, but my wife uses that one when we are both in bed. So I like the Kindle Fire a lot for nighttime reading, but I do not consider it to be a tablet (the screen is too small for web surfing, as well).
Have you looked at the Kobo Glo?
I am a total Kindle fan myself, but when I received the paperwhite, I sent it back because the screen was not as sharp as that of my Kindle Keyboard. Also, the greenish colour of the screen did not exactly turn me on. But ... I had the opportunity to handle a Kobo Glo at an airport display, and I totally loved that screen and the nice blue lighting. If that one could display Kindle books without needing to go the calibre route, I would most likely pick one up.