But I'm surprised he quickly says "No worries you might say, go to Apple and buy a new Mac mini!". If your Mac Mini behaves like he describes, wouldn't the straightforward response be to open it up, give the fans a good cleaning, maybe replace any HDDs with SSDs, and give it a fresh install (of either OS X or Windows 10)? If you blog about tech as this guy does surely it would be no issue at all to just (attempt to) quickly fix these issues.
Don't get me wrong, I too like buying new toys. But I'm amazed at how some apparently tech-savvy people think "this computer does not work as it used to, so it logically follows I should buy a new one!". The problems with his Mac Mini don't sound particularly bad and perfectly fixable in less time it would take to set up a new computer.