I really think it is for me. I just can't see myself buying a tablet that I will mostly use for reading, and it not having retina. Also, the iPad (4th Gen) now has as A6X. The A6 is way faster, and that really shows in certain apps. The mini may not need anything more than an A5 to push the screen, but it will show some sluggishness in some apps for sure.
For ebooks, after the new iPad's retina yes it's a major step down
The A5 processor and 512mb ram (probably 512mb) is also a bit if a misfire.
Worse still, Apple have with the iPad 4th gen announcement being only 6 months caused me frustration and hesitation, it makes me doubt on me as a consumer how long it will be for the inevitable mini upgrades, and to maybe just wait till spring and see if it at least gets the A6 bump too.