I think the OP makes valid points regarding the iPad's cost and configuration factors. I own 2 iPad's after owning several Android tablets first. My favorite tablet is now the iPad. I love everything about them but the configuration and cost given the alternatives makes you think twice about purchasing.
I was ready for an iPad Air but decided against it because 16GB is not enough these days and given the news that the iPad Pro will release next year made we wait for that.
My second choice was the Retina Mini until the price increase. So i'll wait it out as my trusty refurbed iPad 2 runs well enough on iOS 7.
As far as the Kindle HDX, those are nice spec'd tablets that are well built for the cheap, unfortunately you need to be an Amazon customer to enjoy them. I personally do because i'm an Amazon Prime customer and have been for 2 years and the content Amazon now, delivers is pretty stout.
iPad Pro? You're going to wait a year for a device that may not even exist?
If your iPad 2 is still doing the job for you, then more power to ya. No reason to upgrade. But if you're going to struggle for another year to get any use out of it, while spending $200+ on a Kindle to supplement the iPad 2, only to replace them both in a year, I'm not sure I see the logic.
If the iPad is simply a luxury device, then fine, I guess I get it. But if you do actual "work" on it, then I don't see the convenience of splitting that up between two different devices and platforms.
My iPad has replaced my laptop for 85% of what I used to use it for (email, web, Keynote, Pages, PDFs, Evernote), so for me the 128GB iPad Air is a dream come true. After using the iPad Air, I wouldn't want to use my iPad 3 for another year while waiting for an "iPad Pro" that may not ever see the light of day.