The thing is that AMD has stated Zen 3 "will see performance gains as expected for a new architecture", so you're talking 15-20%, and they even threw the figure of 50% higher floating point performance out there as well. IF AMD is able to do this, then previous generation processors get handicapped quite a bit in the resale market. Also, AMD's roadmap shows a 5nm processor with Zen 4, and if a node shrink brings 10-15% performance improvements then Ryzen 3000 series processors take yet another hit in the resale market. Finally, likely with Zen 4 and definitely by Zen 5, a new socket will launch with DDR5, PCIe 5, and USB 4 support. You combine these all with the facts that with core counts are increasing at a rapid pace, it's entirely probable that by the time Zen 5 hits 8 core CPUs will be at the entry level, so you'd be trying to flog a 2-3 year old 12 core processor against a brand new $250 16 core Zen 4 CPU which supports all three major new specs.
So if you want my opinion, don't even think about the resale market, it's going to be such a loss. To put it into perspective, in 2017 I bought a 1800X for the eye watering price of $469.99, mostly because the FX-8350 was ungodly slow in comparison (50% as fast), and because I never believed AMD could improve performance so drastically every generation. When I bought my 3700X and sold my 1800X in March of this year, I was only able to get a pathetic $165, and that's horrendous depreciation even as for as electronics go, but that's because the price of the Ryzen 3000 series had dropped so far and performance increased to such an extent. I only paid $299 for my 3700X, 36% less for a processor with about 36% more performance.
As for Matisse Refresh boost speeds, better wait for the reviews to see if those are actually obtainable in the real world instead of just in specific circumstances, since something like Cinebench R20 single thread is a completely different animal than a professional rendering program or even a game.
