I personally don't feel it's worth it. Anymore than I think an i5 6600k would be worth 100 anything (maybe pesos) over the one before it. The performance improvement per gen is typical, nothing extraordinary.
The new platform has a few advantages, though ddr4 being one of the biggest in reality has little real world impact. Faster m.2 support is nice, if you use m.2 drives. No feature is a benefit if it goes unused, though if planning to take advantage of it can be a perk. End of life is a bit relative. No platform lasts long, a couple of cpu releases and none of which are worth really upgrading to. Typically people stick with what they've got.
For instance no one really upgraded a sandy bridge i7 to an ivy bridge i7. Haswell required a new socket, new motherboard. Boards don't have the longevity they once did, in order for z170 to be 'future proof' means you're considering dumping the brand new 6700k for the 6770k (or whatever comes out next on the 1151 platform). That's not an upgrade, but an expensive side grade. The 4770k to 4790k was very little difference. Not enough to bother with the time to swap the chips.
Either one would be perfectly viable, either one would easily last several (3, 4, 5) years. By then something entirely new will be out with a whole new board, chipset, features etc. Enough to make what people call 'future proof' now look like ancient history which only proves that future proof is a myth.