Not worth the money IMO. The new 2014 Haswell Refreshed i5 is just on-par with the 2012 i7.
See results
http://browser.primatelabs.com/geekbench3/1744122
http://browser.primatelabs.com/geekbench3/1766098
You just get a more efficient CPU without performance boost and faster SSD which is negligible in everyday real work applications, and an Iris GPU which is still way below the performance of a mid-level mobile NVIDIA 650M dGPU. Even Iris Pro can't match the 650M which is 3 Generations behind the 9XXM dGPU.
I would wait 2 - 3 more years before I upgrade where CPU would be double the performance of the 2012 i7, iGPU that can match or be better than the NVIDIA 750M. Heck my 2011 MBA still works amazingly and can hold another 3 years easily since I can edit, convert, 1080p videos fast enough while doing all of my every tasks (web browsing, productivity, video streaming, etc.) without slowing down at all.