One of the things that is different this time around is that for many owners of older systems, the upgrade path carries a bit of a double/triple whammy on the cost front:
-Have to get 8600K if you want to do any sort of proper overclock, no 8400K/8500K available
-No budget motherboard available
-Have to get DDR4 memory, which is a lot more expensive than it used to be
So basically you are talking ~£270 for the CPU and over a ton for both the mobo and RAM (assuming you want 16GB). So that's ~£500 spend even if you don't replace/add any other components. That blows pretty much any base upgrade I've ever done out the water in terms of outlay.
I could kind of live with the CPU price (given the performance) if mobo and RAM were cheaper, but you add all that up and you want a bit more for your money, especially when considering the sort of boosts you used to get from smaller spends. This is speaking for myself of course (5 year old PC), as it depends on what system each person has to being with.