I'm of the opinion that it's only worth upgrading if your either
A) Capping your northbridge transfer rate.
B) Your applications benefit a lot from multi-threading.
With your 1070, I would be suprised if your capping the northbridge, if you are, you may be able to adjust by overclocking it. There's a thread somewhere around here about 'How to tell if your GPU is Northbridge capped' I'm not sure I got the name right, and I can't seem to find it, but maybe someone can point to it. This seemed to be a big problem with 1080ti's on older processors, not so much for 1080's or other graphics cards. It's certainly possible to cap a lessor graphics card with a low end processor, but it didn't seem to be a big issue for most people.
That said, your 4 thread CPU is a bit dated. An 8700K has 12 threads, by that logic we would expect that to be 3x as fast; but there's a lot of applications that are waiting for a response from a single task before they can assign other tasks. Those applications don't benefit from multiple threads as much. I would think if your playing FPS games, or VR, an upgrade would be worth it. I don't have VR, so take what I say with a grain of salt. You could look for benchmarks with the specific games/applications your running, that would provide the most information.
If your a true FPS junkie, you run the latest processor, latest graphics card, and a 240hz monitor. Take every gunfight and know that your reactions should beat theirs. If you lose, you know it's because you need more practice, which is exactly what your doing by taking every gunfight. Shroud does this, and is very successful with it. He's one of the few gamers who takes the time to overclock his CPU, RAM, and GPU... He's also a full time gamer with a pro history in CS go. How much you care depends on you.
Personally I'm running an older 27" 1440p IPS panel (it overclocks to 116 hz). I find I lose a lot of heads up gunfights, when I feel I shot them before I died. As such, I have to play a lot more tactically and give them opportunities to make mistakes. I've been tempted to drop $1800 on a new graphics card and monitor. Unfortunately I don't like the RTX series. A shame, I've got an itch and it's hard to scratch.