Ok, here's what you do. Buy the Air today either i7 or i5 with 256 HD and 8 RAM. (I have the i7 and love it)
Purchase it on an Apple credit card with no interest for 12 months. Take your cash and buy Apple stock. Enjoy the Air and wait for the new version to hit next summer. When the new version becomes available sell your stock and cover your credit card debt. Then dump your old Air to cover the cost of the new one. The probable bump on the stock should cover the discount on the sale of the used Air.
Yes, there is risk with AAPL going down from here, but who cares? Your exposure is minimal and tell me how much fun it would be to have your Air now and the ungraded Air later with Apple paying you for the difference. I would bet you unwind from this deal to have Apple pay for Apple Care on the second machine.
Ok, so today AAPL is at $539.00 Let's see where she's at when the Haswell Airs hit the streets, whenever that is... Good luck.