I'd gladly pay $100 for an extra 2 inches.
Haha
I bought my wife a Mini and loved the form factor. I even said that if it came out with Retina I would buy one instead of another full size iPad.
However, after holding the Air I was sold on it.
My reasons for an Air over a Mini:
I do a lot of school work on it, the bigger screen helps when reading and writing papers.
If I need to I can log in to my work PC with the iPad. Again, the bigger screen helps.
I do not have any clothing or jackets with pockets big enough for the Mini. Therefore, I am not really losing any portability with the Air.