The Rev. B machine is still $550 more than the Rev. A. Is it worth 55% more? Yes - better graphics, more storage, faster RAM, etc.
But the Rev. A is still an excellent deal. As a secondary machine, it's fantastic value. I would rather have the Rev. B, sure, but if I were looking for a machine to complement an iMac or Mac Pro, the Rev. A Air would fit that role very nicely.
Get the rev B, and then upgrade the hard drive down the line when SSD's are cheaper and you'll have a great computer. You buy the rev A, you're stuck there....forever! kinda scary yeah?