I was never bothered by reading on my iPad, though it is superior on the kindle. The question for me is whether the iPad mini provides enough benefits to justify the cost or would the kindle paperwhite be a better fit for me
I suppose we'll have to see what kind of screen it has. If Apple is going to push iBooks with it then I have to think it will be more conducive to book reading than the "big" iPad.
I'm still using my 4 y.o. Sony Reader for books. If the mini screen doesn't burn my irises then I'll switch since I'm already heavily "invested" in apps. Having another iPad around the house would be useful. But I'm skeptical that will happen. If it doesn't then and eInk reader is still the reigning book reading champ.