It all depends on what comes out. I love my new Air and it does everything I need it to, but if something that I seem to like better for whatever reason comes out in say October along the lines of MBPs (which I doubt would pull me in) then I could sell my i5/8/128 for less than $100 loss (pretty close to none). If something that attracts me comes next year in the form of an Air, then I may sell this for around $300 loss and get that.
But next year's model will probably be redesigned, with that follows the bugs of a Rev A product.
I wouldn't at all mind keeping my Air for another 3 years until I go to university and continue to use it as a portable machine along side another Mac (depending on what's available then). I use the Air as a desktop when I'm at my desk and a laptop when I feel like lying down, its really nice.