I currently have an iPhone 5 and iPad 3, and I have decided to get myself an iPad Air 2.
Reason for that is because:
1) I can´t enjoy some of the new features with iOS 8 and Yosemite on my iPad 3 (Hand-off), which I can on my iPhone.
2a) With certain applications cutting off features (Pixelmator) for my iPad. I take it as a sign that the hardware limitations have finally gone too far.
Between my iPad and iPhone, I mostly use the iPad. So it is more important for me that the iPad is more reasonable up to date.
Perhaps I would have used my iPhone more if the display was larger. Still I rather wait for next version. Giving the developers some time to optimise their apps for the larger displays, and giving the banks in my country more time to implement Apple Pay.
Edit: Pixelmator just released an update allowing more devices use the repair tool.