I sold my MBA (2011) i7, 256gb / 4gig today a couple of hours ago on CL for $1,100 (asked $1,200).
Mine was in mint condition and had one month of AC left on it. Listed at 8:30 this morning and had the cash by noon. Several interested parties emailed...so definitely a good chance to get that much if you decide to sell.
The new MBA with my EPP discount is $1,594 (for 2.0ghz / 8 gig ram / 256gig drive). So I would net out at about $500 for the upgrade with another year of AC.
AC for year is worth ~$125 (half of what a 2 yr AC would cost)
8gig of Ram over 4 = $100 (per the pricing for the new one)
2.0ghz over 1.8ghz = $100
Free upgrade to Mountain Lion - $20
So I am getting $345 more stuff for $500 (which in effect makes the net cost for a better graphics chip, USB3, faster SSD, quiter fan, 1 yr newer battery, etc = $155).