My wife has had an iPad 2 since it was released and I purchased an iPad Air this past fall (upgrading from an iPad mini). The two biggest improvements one would notice going from a "2" to an Air is the screen resolution and lower weight. After using an Air it would be difficult to use a "2" due to the lower resolution. I felt the iPad was too heavy to be an e-reader, hence why I had the mini, but now the Air with the Smart Cover is not much heavier than my Mini with it's cover (which was a very sturdy, hard cover.
If you can hold out until the "Air 2" comes out, you will probably get the Touch ID fingerprint reader. I mostly use the iPad at home, so I don't mind not having it, but if it went out of my house a lot, and hence at greater risk of loss or theft, I'd like to have it.