I'm a computer repair person and your current Dell sounds like it's lived its useful life. I would trash it--after removing/backing-up any personal data, of course
And unless you really want/need a retina display, I'd definitely get a new (or refurb) 2013 model Air now. We are still probably at least 6 months or more away from a new Air--if not more. Also there is no guarantee that the new one would even have a retina display.
I have the 2013 11.6 model and I love it, no issues with the screen not being retina. And, yes, I have an iPhone 5 with retina and an iPad mini retina and I don't ever feel that using the laptop (which I do a lot) is bad with its non-retina screen.
Also, if you want the 13" model, now would be the time to get it, since some of the rumors on this site and others are suggesting that there may only be a 12" (or 11.88") model. Just a rumor, but it's a possibility.
Just my two cents! Good luck.