I bought mine used a few months ago. Great upgrade from the 2014 Mac mini, and I think it will tide me over until the remainder of Apple Silicon rollout finishes.
It is a 2009, and a previous owner bumped the memory up to 24 GB, there is an SSD (512 GB) and three HDD (1 TB each). Also, best of all the processor was upgraded to a 6 core 3.33 GHz Intel Xeon and the firmware was already at the latest version.
The only thing I could realistically considering to increase the power would be to swap out the single processor board for a dual processor board, but those are going for at least $500 - $600, with no memory. Little too much to spend (well, I tell myself that).
[Edit: So I saw that "blur" on the lower front of the computer after I uploaded the picture. So I look at it closer and run my hand over it. It was a bunch of white cat hair that got sucked onto the front grill. 🙀]
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