Are there enough new tech in the platforms (i.e. USB C or newer PCI-E) to warrant a full mobo + cpu + ram upgrade?
That's really up to you. Are you going to use any of that tech? I mean, if you upgrade to Z490 now, you're still on the same PCI-E 3.0 as your 6700K. Of course, the boards are supposed to be able to do PCI-E 4.0 when the next generation CPUs come out, but I'm not holding my breath. Intel tried this before, and actual support was problematic.
As for other things like USB-C, better WiFi, 2.5Gb LAN(though that's not a guarantee) well, again you have to ask if
you are going to use those things right now.
Is 16GB of ram still okay in 2020 or will 32GB finally make a difference in day-to-day use
You can re-use the RAM you have now. You'll be fine.
Will upgrading to the newest SSD feel "noticeable" from a Samsung 950 pro
No. Even "experts" have hard time determining the difference between a SATA, PCI-E 3.0, and PCI-E 4.0 SSD in a blind test. Right now, there is no point in wasting money on a PCI-E 4.0 SSD.
So I've been sitting on 6700k + 16gb for some time now given that each gen only represents something like 5-10% performance increase in CPU intensive tasks and near 0% increase in gaming at high resolutions. However, with the new generation of Intel CPUs coming out and the latest Ryzen, would it be beneficial to finally upgrade?
I put this one last because it probably is going to receive the most discussion. The 5-10% improvement in CPU intensive tasks is only if those tasks are single threaded. If anything you do is multi-threaded, there have been huge gains. Hell, I still have a 7700K, and it has been relegated to doing light duty in a media center PC. Even my 8700K just crushes the 7700K in the CPU intensive tasks I do, and the 10850K is a beast(you'll find the same thing on the AMD side too).
That said, most games still don't go over using 4-Cores. So gaming improvements have been minor, especially in AAA titles that are very graphics intensive because the GPU is usually the limiting factor. The thing is, if you look at a i3-10100 which is very close to your 6700K spec wise, the 10100 is only 4% slower than the 10900K at 1440p resolutions when using a 2080Ti and its 1% slower at 4K. That comes down to the fact that even the 2080Ti is the limiting factor at those high resolutions.