Worth upgrading from Rotel RC-1572 to the new RC-1572MKII ?

The New ones are ROON certified.  Might be worth it just to try out that.  But also has a bunch of other refinements. 

I really don’t know much about Roon. I’ll have to read up. Clearly I’m behind the times.

Its basically like a big library music interface to you existing service.  If you enjoy music discovery its the best.  If you just want to queue up and album and hit play its not worth it.   Cost you some $ to set up as well.

Without doing a deep dive on what they upgraded on the 1572, I would be surprised if you noticed an huge difference. If you want to stay with Rotel, I would go for the 1590. Preamps have a huge impact on your system, you might look around and see what else is out there in your price range. Consider a used solid state preamp, and for the same price you might be able to bump your system up to a new level. 

Are you using the DAC in the Rotel or the one in the Nano? What type of cable are you using to connect? In either case, the DAC’s in these units are afterthoughts, an upgrade there might be worth considering.