I have a 2013 11" i7/8gb/512gb MBA and love it. Plenty of computing power for ordinary use and it even holds it own with Final Cut Pro and Logic (although I now have a 2012 quad mini dedicated for that). Battery has definitely declined, I used to get around 10 hours, now I think it would go 5 or maybe 6 (based on estimates after two or three hours use).
It's a fantastic computer for travel, but I've been more of a stay-at-home type for the last couple years, so it's usually plugged in. Recently the trackpad has been showing its age. I know this can be caused by a swelling battery, but there's no visual evidence of that. I prefer using a mouse when possible anyway, so it's not much of a big deal.
But when the battery finally needs replacing, or if I start travelling again, I'll probably just replace it (not sure what with). I guess a couple hundred bucks could fix whatever is needed, but it's looking old and beat up and I'm not keen on sinking money into 5 year old computers. This is the longest I've kept a Mac laptop - and my first was a PowerBook Duo! 🙂