Just purchased a MBA i5 w/256gb and thought I'd chime in. This is my first macbook air, and it's replacing a 2010 15" 2.4ghz i5 macbook pro and a custom built gaming rig from 09' with then almost top of the line components.
I did not get the RAM upgrade or the processor upgrade because I did not find a need for either. In this machine I was either going to have both upgrades or none, and I realized that I am never going to use the extra juice the upgrades would give me so why bother paying an extra 180+tax?
I am currently in my junior year at USF and am running a start up company that myself, my brother, and a friend have founded. Normally I would bring my MBP to school and to the office and have the desktop at home for music and movies. Being that I no longer game on the PC (strictly xbox these days, when I do get to play), I am opting to get rid of the desktop. All the music and movies I want can be stored on the MBA and external USB 3.0 drives. There are also no audio/visual problems because the MBA can power a 1080p TV and surround sound system no problem.
Would I like to have the top of the line model? Yes, but to me the extra 200 or so dollars in my pocket is worth it, and if the next MBA has significant upgrades I'll probably sell the one I have and get the next one. I decided on the MBA because going from home/school/office/client offices, switching from brief case to backup, having textbooks or whatever else I may have on me, I've found that portability and form factor are very important to me.
When my needs change again I'm sure I'll find a setup that suits them. Hope this helps anyone in a similar situation.