I went from a 2008 15" MBP 2.4ghz to a 2011 13" MBA and it was a huge upgrade in terms of speed. The SSD makes a big difference in everything, and the CPU is about twice as fast.
As for whether it's right for you or whether that's a good deal…. I don't know. The 2012 models are not as desirable as 2013 or newer, mainly because they have much shorter battery run time. A 2013 MBA will run almost twice as long on a battery charge...