I was selling Mystics when they were new. In my short tenure with BMW, it was the transition from Airheads to Robo-Boxers. The Mystics were pretty much the very end of the Airhead line in North America and specifically the USA. I am pretty sure the Airheads continued in G/S trim in other parts of the globe.
If memory serves, I wasn't too hot on them. Strange access to tools; you need a tool to remove the side cover, luggage mounts were a bit fiddly, and other stuff.
Still. It's an air cooled boxer engine. Pretty much the zenith of BMWs many years of air cooled motorcycles. It's not a bad starting point, and I would let one lounge in my garage.
That said, a 75/5 would also be a happy addition to the Church. I love my RS and Das Beast, and the R60/2 is a fine machine, but there is always room for one more airhead.
'66 BMW R60/2, '83 BMW R100RS,'81 BMW R100RS "Das Beast", '87 BMW R850R '77 Honda XL125