I'm still using my 2011 mac mini. I have the base model with the i5 CPU, HD3000 graphics, and it started with 2GB of RAM and a 500GB hard disk.
Over the years, I've always run the latest OS on it, I have 8GB of RAM in it and I have a 240GB SSD in it.
I have yet to run 10.12 on it, but with 10.11, it's a good system. I keep several Safari tabs open, Outlook/Word/Excel/OneNote 2016 are open almost all the time, and I do some video editing sometime in FCP6.
I haven't done Lightroom on this system, but Aperture and Photos have been fine when I tried them. The system I've spent most time in Lightroom on over the years has been an older Core2Duo Windows laptop, so I have no trouble believing it would work well.
If you haven't already bought one, or just generally food for thought: I wouldn't personally bother with any of the Radeon-equipped Mac minis. Since ~2009 or so I haven't seen any good evidence on either the PC or Mac side of things that discrete GPUs with only 256MB of memory make a meaningful difference in game performance, and I don't think it will make a meaningful OpenCL contribution. The 256M Radeon might play certain older or lower performance games better (I'm thinking in particular of World of Warcraft) than the HD3000 or HD4000, but it won't let you really step up to a higher tier of gaming.
Depending on what your budget is -- if you can pull together enough money to buy one of the higher end versions of the 2014 Mac mini, that'll probably last longer overall, but if you need slightly more CPU horsepower in general, the 2012 Ivy Bridge Mac mini with the quad-core CPU has a quad and some more expansion options, including dual SATA disks, USB 3.0, ThunderBolt 2, and up to 16 gigs of RAM.
If you were going to get most of that anyway and can spring for a 2014 mini pre-configured that way, it shouldn't be a bad system. The real trouble is that the 2014 Mac minis are all on Haswell chips. No word yet on whether there will be a real 2016 or 2017 Mac mini with Skylake CPUs.