I have floated around the idea of getting the 2015. I will need to look for some side-by-side comparisons and decide. I would love the retina screen and the ability to hook it up to my 4k monitor, though (when compared to my 2011). This may be the one time I might prefer last year's model.
I read here - and elsewhere - about the rMB (and indeed, rMBP).
To me, the thing about the MBA is that - finally - and it did take several iterations - they made the perfect computer.
This is a fantastically reliable computer. For a long time, - until 2013 - the MBA had yet to live up to its promise, but once Apple gave it sufficient power, memory, reliability, and a fantastically improved battery life, the machine was unbeatable for anyone who needed something powerful and portable and who was constantly on the go.
To my mind, the rMB still needs a lot of improvement; I don't doubt that it will happen, - eventually - but it hasn't happened just yet.