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The iPad Air does well under iOS 8.1.2.
While the main advances on iOS 8 are not obvious at first glance, there are a lot of nice features to improve moving files between apps and putting third party widgets in the Today view of Notification Center. They also introduce third party keyboards.
There are some improvements to the native apps, like a timer for the camera, slo-motion video, rich text in the Notes app, etc.
You probably won't miss them, unless you see them being used, and then the itch to upgrade will start.
Just be prepared for a few things to change.