I think it's the most bang for the buck upgrade on the Air.
I would agree with others that the $100 for the extra 4GB is probably the best upgrade for the price. That said, most people won't need it. I got it because I like to run Windows on my MBA as well and I would prefer being able to dedicate the extra RAM to the VM.
Since the RAM is soldered onto the machine, it makes sense for me to get it now, since I can't get it later. With the SSD, although there is currently no 3rd party for anything different, it can technically be replaced. I expect OWC to have something in the not too distant future. So if in two years I want something with higher capacity, I could probably go that route and replace it. But RAM you're stuck with.
Do some apple stores sell the base 13 with 8 gigs? Because I'm splitting the cost with my mom and she tends not to like to buy things online.
On other threads about memory people have said that Apple stores don't have 8GB models. One user said that a NY store stocked them, but most don't seem to.
Just get your mother to give you the funds and then buy from the online store.
I had a harder time shelling out for the 256GB SSD. But decided to do so because 128 is just too small.
In all honestly, for light PhotoShop, web browsing and MicroSoft Office, you won't notice the difference between 4gb and 8gb RAM.
However, if in the future you scale up your work load, 4gb RAM might bottleneck your system. Upping to 8gb RAM future proofs your laptop, specially considering it's just $100.
Story of my life right now. I am still waiting on an i5 versus i7 benchmark to purchase my MBA, but for a long time I struggled between whether or not to get the 256 GB SSD. I didn't even think twice before getting more RAM, though.