The xeon is the same price as a Ryzen 2700 or an intel 8400.
They definitely beat it on power usage.
This all makes the argument really depend on how much utilization you think the xeon will have.
If you plan to run it 24/7 100% utilization (or as close as you can get), yes new hardware makes sense. (There's definitely a cost reason that these companies are ditching their old xeons for new ones, it saves them money and rack space).
If you're playing around for a few hours in the evening and on weekends (as suggested), it'll probably be a maximum of $10 per year in power costs.
So I think even with power costs, having run the numbers, these processors do make an attractive alternative to newer hardware. They are comparable and at a comparable price on the market, but if you can get a deal by bargain bin hunting, they can be a great value. It is unsurprising that the $/performance is very similar, that is how arbitrage markets are supposed to work.
There are some pitfalls here that are not mentioned, while the processor itself can be cheap, it is often the case that server grade motherboards are more expensive. This is particularly true with older Xeons, where people are trying to repair things that have broken. There's kind of a curve where demands drops up until a point and then the supply drops (people scrap things for the metal content rather than reselling)... so price starts to creep up again. This shouldn't be a problem.
The other issue is that you end up with hardware compatibility issues. Can I stick my new graphics card in the old xeon box? Probably(?) can I do something more exotic or new? maybe not? Again this shouldn't be an issue.
The hardware compatibility thing almost bit me. I have an older dell t3600 that a bought a new Radeon 480 GPU for. I only verified that the power supply could handle it and the pci slots were compatible. The card “fit” but I couldn’t put side cover back on, because there is a handle riveted to the inside of the side panel that collided with the card. I ended up having to drill out the rivets and remove the handle.
The xeon is the same price as a Ryzen 2700 or an intel 8400. They definitely beat it on power usage.
This all makes the argument really depend on how much utilization you think the xeon will have.
If you plan to run it 24/7 100% utilization (or as close as you can get), yes new hardware makes sense. (There's definitely a cost reason that these companies are ditching their old xeons for new ones, it saves them money and rack space).
If you're playing around for a few hours in the evening and on weekends (as suggested), it'll probably be a maximum of $10 per year in power costs.
So I think even with power costs, having run the numbers, these processors do make an attractive alternative to newer hardware. They are comparable and at a comparable price on the market, but if you can get a deal by bargain bin hunting, they can be a great value. It is unsurprising that the $/performance is very similar, that is how arbitrage markets are supposed to work.
There are some pitfalls here that are not mentioned, while the processor itself can be cheap, it is often the case that server grade motherboards are more expensive. This is particularly true with older Xeons, where people are trying to repair things that have broken. There's kind of a curve where demands drops up until a point and then the supply drops (people scrap things for the metal content rather than reselling)... so price starts to creep up again. This shouldn't be a problem.
The other issue is that you end up with hardware compatibility issues. Can I stick my new graphics card in the old xeon box? Probably(?) can I do something more exotic or new? maybe not? Again this shouldn't be an issue.