Pointless. An i3 8100 would dump half the heat, use half the power, and be at least twice if not three times faster. You can tell when the snap is missing off old boxes. Everything has gotten fatter - code, the Internet, you.
Faster at what, exactly? I boot into my OS in about 15 seconds (it takes me longer to log in than it does to get to the log in point). Off an ssd, the only thing that isn't instant is the internet connection, which out in the country here is kinda slow. I notice zero difference in 'snappyness' with this x4, tight timings 16GB ram, running boinc 100%, versus any of my newer builds (4.8ghz direct-die richland running 2400mhz ram).
An i3 system with 16gb of ddr4 is going to cost me at least $400 cad (being optimistic), it would take 100 years to pay itself back in the maybe 10w idle power difference. Plus, I'd need to skimp on board and ram quality to get there for even close to $400, so it probably wouldn't be as reliable either. All this for quality of life downgrade (loss of overclocking).
Lastly, what fun is an i3-8100? Locked, no baseclock fun, ram doesn't do anything either. If I'm going to throw money at an 'upgrade', its going to actually be an upgrade that will last another 10 years like the processors in this thread, and let me have fun like most of the old hardware too.
For what most of these machines are - web browsing desktops - upgrading to a solid state if its not already would be the only noticeable improvement, besides a good cleaning to keep coolers happy.