Well I noticed that Launchpad fade in / fade out is sometimes sluggish. Doesn't go away with reinstalling or any other way.
I use my MBA mainly for Websurfing, Skyping, light image editing, and Movies.
My main idea was that i either pay 250€ for apple care or sell my MBA and use the money for a new MBA.
New MBA release doesn't make your old MBA slower, though. So if the current MBA is serving you fine, why should you? .
And regarding you above use cases, I would say wait for Air 2013 like me (I upgrade from base 11" with 4GB to ultimate 11" last week )