I swapped out my 2012 i7 for the i5 256gb over the weekend. Seeing the benchmarks for the i7 I didn't think it justified an extra $200. Those extra 2 cores make a huge difference even without hyper-threading. I am hoping this thing will sit quietly in its spot and not trouble me until 2024. I may treat it to a GPU in 2020 if it behaves itself.
I made the same move and enjoying the new Mac mini a lot. I installed 16gb and a ssd in my 2012 model and it was pretty darn fast. This new mini(i5) feels so much faster with the new cpu. I will eventually install 32gb of ram.