Yes, I agree with the first 3 with a but at the end... I've installed 10.11 B2 on my 2012 i7 Mini Server's second hard drive and it's connected to a Dell P2715Q display - IMHO it's pretty serviceable, with the display looking nicer and responding much better than with Yosemite. I also use an iPad and Duet for minor operations on the Server.
And, if one's Mini needs a bit more "oomph" or a larger desktop, Matrox just came out a couple of months ago with two new versions of their eGPUs that support Yosemite and multiple displays. So we can get some more time out of our Minis!