For me it is the little things in each new Upgrade to Photoshop that improve my working-speed, efficiency and comfort which are just as important as newly introduced tools and features.
I have always upgraded immediately and see no point in delaying to do so – particularly now that the subscription price is so reasonable.
ACR and Ps CC 2014 are now faster and more stable than any previous version that I have ever experienced.
That's always been my view. But too many people can't see past the 'wow' features and never think to look at the refinement aspects, which usually have the most overall impact on PS users ease of use.