I'm still working (happily) from my maxed out 2012 11" Air. I put a new battery in it earlier this year and upgraded the SSD last year. You can definitely get longevity out of the laptops. My work undulates between email, text editors, Perl, C#, and whatever I do while SSH'ed into servers. None of that requires much in the way of CPU. Maybe if I was an iOS developer or did some other creative work I'd have a different opinion.

The new Air may be enough for me to upgrade (mostly for the Retina Display), but that's mostly because I can rather than because I need to.