Thanks for the feedback.
I try to replace my Mac every 18 months. I tend to get a great re-sale value since I have AppleCare to include.
Based on the Haswell feedback I'll likely hold off another 6 months! Of course, my re-sale value will go down when there is a new announcement...but oh well.
The old cliché about 'buy if you need, wait if you merely want' is the advice I would offer. For now, the specs on your machine sound pretty impressive to me, given that any upgrade you are likely to make before rumoured (note, rumoured) upgrades occur, will be, at best, fairly incremental.
As you have Applecare, you can afford to wait a few months and then see what the summer brings.
My own position is slightly different as my MBA is 28 months old, a year older than yours, so any change I make over the next few months will be quite noticeable.
Of course, resale value goes down every time there is an upgrade, - despite Applecare - or a significant change in the product line. That is life, and that is also the price you pay for acquiring a significant upgrade in computing power or radical innovation in technology.