Thanks for your advice.
I probably had Rompr working before setting Mopidy up properly but short of starting with a fresh SD card it was mission impossible to get Rompr to update. I had reinstalled Mopidy and Rompr with no success.
I've used the latest Mopidy for the Raspberry Pi and it is using Python 2.7. I could not find a version that uses Python 3. The Modidy extensions I installed are based on Python 3 and were not showing up as available. I did reinstall Mopidy a few times. I think there is an option to build it yourself and that may work.
Using MPD, Rompr updated quickly and intuitively and does what I need.
I realise that Mopidy supports Spotify and other online stuff but my objective is to use Snapcast as a multi-room speaker. Spotify via Rompr/Mopidy plays locally and is just a useless distraction in my case.
Family members like to take over and play music from their phones. They mainly use Spotify. I have setup my "master speaker" Raspberry Pi to act as a Bluetooth speaker and push the audio to Snapserver and therefore all of the multi-room speakers running Snapclient.
I'm getting everything I need using MPD and Rompr so will stick with that.
Congratulations on your great work.