My 2009 machine is still working well enough so why wouldn't a 2012 machine be a good choice. Our 2012 MBP works well esp with SSD now added. A similar vintage iMac is a decent choice or a new 27" 5K. The current Mini's are in my view not worth the new price money. As my 2009 Mini won't run Sierra by late 2017 I'll be two OS behind
My mid-2011 iMac with 20 gigs of RAM and SSD HDD setup also runs very well indeed. However, I wouldn't go out and buy one of that vintage now as I would be buying old tech. Many of Apple's devices arrive new from the factory with 'old tech' so by the time they are a few years old the tech inside them is even older.
If you add the fact that by the time you purchase your 2012 Mini (2017 according to your statement) it will then be five years old so will not be supported much beyond that. None of this makes it a wise purchase.