It depends on one's use cases. I use an iPad Air for two main tasks: 1) to sketch and "paint" (using ArtRage); and 2) to make music in various apps. For these applications, screen size trumps portability (larger canvas for art, wider screen for audio timelines and more keys on keyboards).

I don't think I'm going to upgrade anytime soon, but when I am looking for a newer tablet, the iPad Pro will tempt me.