Well, here's what I would point out in response to your inquiry. First, the newer systems allow not only much faster memory, but a lot more of it. You can put 64gig's of very fast DDR4 into a new system, and you will not run out of memory. This is another great function of upgrading, as the older chips didn't allow for as much memory.It's less the speed of the memory and more the quantity of it I haven't noticed much difference with memory speed - haven't done any conclusive tests though... I can build a fairly high spec PC and money isn't an issue. I'm just finding it hard justifying getting a 16 thread CPU - is there anything that needs it?
My old computer had an i7 processor, and 16gb's of memory running around 1800mhz... I noticed a considerable difference when I built my current machine a few years ago, put a Ryzen 7 1700 processor in it, and was able to not only overclock that processor all the way up to 4ghz, but also my 32gb's of memory up to 3466mhz. My entire system zipped around like it was on steroids. Now I consistently run 15-18 projects at the same time with virtual machines, and never run out of memory or processor power. So by upgrading, you allow your system so many improvements throughout computing, especially for multitasking processor intensive projects. But the main reason why all those threads and cores are going to benefit you is that everything is moving in that direction. You will future proof your system. Now that all the newer chips are in a core/thread war, dev's are starting to write software to take more and more advantage of those extra cores and those extra threads. So while you might not have a reason at the moment for those threads, six months from now, there surely can be one.
For as cheap as the 3700x is, how efficiently it runs and all of the benefits it would bring to your computing, I could easily rationalize upgrading.