Well I have the 2011 Macbook Air now, so I am definitely not upgrading for minor speed bumps and such. I don't really use USB stuff at all nor do I own any USB 3.0 devices, so that's unimportant. And the space/power I have is enough for what I use it for (mostly office work, internet browsing, etc.).
I would definitely upgrade for a retina display though. I saw the new Macbook Pro Retina at the Apple Store today and it was hot! But its too big, so I won't be getting it.
I learned from being an early adopter of technology that when you buy this early, you pay all the premium and you don't realize all the benefit. Just like with the retina display, it will take 6 months to a year for apps to really take full advantage of it so by the time they do you'll be able to have it cheaper and in the device you want.
So when it comes to the Air, at the same price point as the current air ($1199 for a 13" Retina), I will buy it.
I would note though that if I *NEEDED* a laptop right now, I'd buy one of the Airs thats out there and not suffer waiting for a retina one since we have no ETA on it. I would also bet it will be at least a year before it hits the Airs, as they need to improve battery tech. The small chassis on the air leaves little room for more battery power and I would not buy a Retina MBA with 3 hours of battery life. It Must be the same or better.