Same, the bang for buck on a 5yo server is insane. I got an old Dell a year ago (to replace our 15yo one that finally died) and it was $1200 AUD for a maxed out recently-retired server with 72TB of hard drives and something like 292GB of RAM.
Seriously. 24/7 adds up faster than most realize!
The idle wattage per module has shrunk from 2.5-3W down to 1-1.2 between DDR3 & DDR5. Assuming a 1.3W difference (so 10.4W for 8760 hours), a DDR3 machine with 8 sticks would increase your yearly power consumption by almost 1% (assuming avg 10,500kWh/yr household)
That's only a couple dollars in most cases but the gap is only larger in every other instance. When I upgraded from Zen 2 to Zen 3 it was able to complete the same workload just as fast with half as many cores while pulling over 100W less. Sustained 100% utilization barely even heats a room effectively anymore!
A similar one I just ran into: my Framework Desktop was idling @ 5W more than other reported numbers. Issue turned out to be the 10 year old ATX PSU I was using.
The one thing to be careful with Zen 2 onwards is that if your server is going to be idling most of the time then the majority of your power usage comes from the IO die. Quite a few times you'd be better off with the "less efficient" Intel chips because they save 10-20 Watts when doing nothing.
To be clear, this server is very lightly loaded, it's just running our internal network services (file server, VPN/DNS, various web apps, SVN etc.) so it's not like we're flogging a room full of GeForce 1080Ti cards instead of buying a new 4090Ti or whatever. Also it's at work so it doesn't impact the home power bill. :D
Just not too old. Easy to get into "power usage makes it not worth it" for any use case when it runs 24/7