iPad – revolutionary device, yes the Air is absolutely worth it. Very few deals (if any) best way to get one cheap is to buy it in the US, about 40% cheaper mail order or via a deal at somewhere like BestBuy. I think 32gb is a decent size, you cannot add memory later and 32 allows good amount of movies, music, photos, documents etc. if you do get a Mini get retina, no point buying older technology processor in cheaper one. As an additional thought if you have a tv with hdmi an Apple TV (£100) can change the way you watch content, eg bbc iPlayer catch up from iPhone (or pad) onto tv, rented content from netflix or itunes, midweek mini movies look great too
I have an original iPad 1 and use it every day, after getting it I got rid of my laptop and kept iPad and desktop computer. I do chuckle about portability argument of the Mini vs Air, my Pad1 is a relative “brick” vs current iPads and I can hold it effortlessly, I mean come on it weights nothing ! The Mini fits more conveniently into a large coat pocket or a ladies handbag (so perhaps good for the wife) I admit but I prefer larger screen of full size. I have not upgraded as each model has come out as I’ve not seen the point but the new Air is a big step forward so will be upgrading on my next trip to the US.
As for android if your wife likes her iPhone stick with Apple, the more devices you get the happier you’ll be as its the “working together” element which is a big strength.