I'd cancel and see about doing a little poly-fill and sand. If it still looks like hell then maybe get it fixed.
Or
Don't do anything. Wait until the next revision. Sell it on eBay for $1500 and then buy a new one. The 120G single platters are supposed to be out soon. So you'll see a bigger hard drive and possibly a 2.0 processor. That way you'll only be out $300 and you'll have a better machine.
You can almost guarantee that someone will give you $1500 for a worn Air.
Are you kidding me? Maybe $1100 at the most.
Who in the right mind would buy something that's got a dent for $300 less than new? Might I add, without warranty.