I use a Optiplex 3060 now (though about to sell it), same processor, upgraded to 64GB of ram (yes it works, even though the spec sheet says 32GB max). I've been running 4 VMs and about a dozen containers with no trouble.
The biggest downsides are lack of SATA ports for connecting a lot of drives, and only a single 1GB nic.
If the price is right, it is a great low power server.
Pretty handy looking, but an SFP+ port would be better than the 10gbe rj45.